 




I n the previous chapter, we looked at life processes involved in the

maintenance functions in living organisms. There, we had started with
a notion we all have, that if we see something moving, it is alive. Some of
these movements are in fact the result of growth, as in plants. A seed
germinates and grows, and we can see that the seedling moves over the
course of a few days, it pushes soil aside and comes out. But if its growth
were to be stopped, these movements would not happen. Some
movements, as in many animals and some plants, are not connected
with growth. A cat running, children playing on swings, buffaloes
chewing cud – these are not movements caused by growth.
Why do we associate such visible movements with life? A possible
answer is that we think of movement as a response to a change in the
environment of the organism. The cat may be running because it has
seen a mouse. Not only that, we also think of movement as an attempt
by living organisms to use changes in their environment to their
advantage. Plants grow out into the sunshine. Children try to get pleasure
and fun out of swinging. Buffaloes chew cud to help break up tough
food so as to be able to digest it better. When bright light is focussed on
our eyes or when we touch a hot object, we detect the change and respond
to it with movement in order to protect ourselves.
If we think a bit more about this, it becomes apparent that all this
movement, in response to the environment, is carefully controlled. Each
kind of a change in the environment evokes an appropriate movement
in response. When we want to talk to our friends in class, we whisper,
rather than shouting loudly. Clearly, the movement to be made depends
on the event that is triggering it. Therefore, such controlled movement
must be connected to the recognition of various events in the
environment, followed by only the correct movement in response. In other
words, living organisms must use systems providing control and
coordination. In keeping with the general principles of body organisation
in multicellular organisms, specialised tissues are used to provide these
control and coordination activities.

      

In animals, such control and coordination are provided by nervous and
muscular tissues, which we have studied in Class IX. Touching a hot

 Science

2019-20
object is an urgent and dangerous
situation for us. We need to detect it,
and respond to it. How do we detect that
we are touching a hot object? All
information from our environment is
detected by the specialised tips of some
nerve cells. These receptors are usually
located in our sense organs, such as the
inner ear, the nose, the tongue, and so
(a)
on. So gustatory receptors will detect taste
while olfactory receptors will detect smell.
This information, acquired at the
end of the dendritic tip of a nerve cell
[Fig. 7.1 (a)], sets off a chemical reaction
that creates an electrical impulse. This
impulse travels from the dendrite to the
cell body, and then along the axon to its
end. At the end of the axon, the electrical
impulse sets off the release of some
chemicals. These chemicals cross the
gap, or synapse, and start a similar (b)
electrical impulse in a dendrite of the next
Figure 7.1 (a) Structure of neuron, (b) Neuromuscular junction
neuron. This is a general scheme of how
nervous impulses travel in the body. A
similar synapse finally allows delivery of such impulses from neurons to
other cells, such as muscles cells or gland [Fig. 7.1 (b)].
It is thus no surprise that nervous tissue is made up of an organised
network of nerve cells or neurons, and is specialised for conducting
information via electrical impulses from one part of the body to another.
Look at Fig. 7.1 (a) and identify the parts of a neuron (i) where
information is acquired, (ii) through which information travels as an
electrical impulse, and (iii) where this impulse must be converted into a
chemical signal for onward transmission.

 
 Put some sugar in your mouth. How does it taste?
 Block your nose by pressing it between your thumb and index
finger. Now eat sugar again. Is there any difference in its taste?
 While eating lunch, block your nose in the same way and notice if
you can fully appreciate the taste of the food you are eating.

Is there a difference in how sugar and food taste if your nose is

blocked? If so, why might this be happening? Read and talk about
possible explanations for these kinds of differences. Do you come across
a similar situation when you have a cold?

Control and Coordination 

2019-20
 
‘Reflex’ is a word we use very commonly when we talk about some sudden
action in response to something in the environment. We say ‘I jumped
out of the way of the bus reflexly’, or ‘I pulled my hand back from the
flame reflexly’, or ‘I was so hungry my mouth started watering reflexly’.
What exactly do we mean? A common idea in all such examples is that
we do something without thinking about it, or without feeling in control
of our reactions. Yet these are situations where we are responding with
some action to changes in our environment. How is control and
coordination achieved in such situations?
Let us consider this further. Take one of our examples. Touching a
flame is an urgent and dangerous situation for us, or in fact, for any
animal! How would we respond to this? One seemingly simple way is to
think consciously about the pain and the possibility of getting burnt,
and therefore move our hand. An important question then is, how long
will it take us to think all this? The answer depends on how we think. If
nerve impulses are sent around the way we have talked about earlier,
then thinking is also likely to involve the creation of such impulses.
Thinking is a complex activity, so it is bound to involve a complicated
interaction of many nerve impulses from many neurons.
If this is the case, it is no surprise that the thinking tissue in our
body consists of dense networks of intricately arranged neurons. It sits
in the forward end of the skull, and receives signals from all over the
body which it thinks about before responding to them. Obviously, in
order to receive these signals, this thinking part of the brain in the skull
must be connected to nerves coming from various parts of the body.
Similarly, if this part of the brain is to instruct muscles to move, nerves
must carry this signal back to different parts of the body. If all of this is
to be done when we touch a hot object, it may take enough time for us to
get burnt!
How does the design of the body solve this problem? Rather than
having to think about the sensation of heat, if the nerves that detect heat
were to be connected to the nerves that move muscles in a simpler way,
the process of detecting the signal or the input and responding to it by
an output action might be completed quickly. Such a connection is
commonly called a reflex arc (Fig. 7.2). Where should such reflex arc
connections be made between the input nerve and the output nerve?
The best place, of course, would be at the point where they first meet
each other. Nerves from all over the body meet in a bundle in the spinal
cord on their way to the brain. Reflex arcs are formed in this spinal cord
itself, although the information input also goes on to reach the brain.
Of course, reflex arcs have evolved in animals because the thinking
process of the brain is not fast enough. In fact many animals have very
little or none of the complex neuron network needed for thinking. So it is
quite likely that reflex arcs have evolved as efficient ways of functioning
in the absence of true thought processes. However, even after complex
neuron networks have come into existence, reflex arcs continue to be
more efficient for quick responses.

 Science

2019-20
 Figure 7.2 Reflex arc

Can you now trace the sequence of events which occur when a bright
light is focussed on your eyes?


Is reflex action the only function of the spinal cord? Obviously not, since
we know that we are thinking beings. Spinal cord is made up of nerves
which supply information to think about. Thinking involves more
complex mechanisms and neural connections. These are concentrated
in the brain, which is the main coordinating centre of the body. The
brain and spinal cord constitute the central nervous system. They receive
information from all parts of the body and integrate it.
We also think about our actions. Writing, talking, moving a chair,
clapping at the end of a programme are examples of voluntary actions
which are based on deciding what to do next. So, the brain also has to
send messages to muscles. This is the second way in which the nervous
system communicates with the muscles. The communication between
the central nervous system and the other parts of the body is facilitated
by the peripheral nervous system consisting of cranial nerves arising
from the brain and spinal nerves arising from the spinal cord. The brain
thus allows us to think and take actions based on that thinking. As you
will expect, this is accomplished through a complex design, with different
parts of the brain responsible for integrating different inputs and outputs.
The brain has three such major parts or regions, namely the fore-brain,
mid-brain and hind-brain.
The fore-brain is the main thinking part of the brain. It has regions
which receive sensory impulses from various receptors. Separate areas
of the fore-brain are specialised for hearing, smell, sight and so on. There
are separate areas of association where this sensory information is
interpreted by putting it together with information from other receptors
as well as with information that is already stored in the brain. Based on

Control and Coordination 

2019-20
 all this, a decision is made about how to respond and the information is
passed on to the motor areas which control the movement of voluntary
muscles, for example, our leg muscles. However, certain sensations are
distinct from seeing or hearing, for example, how do we know that we
have eaten enough? The sensation of feeling full is because of a centre
associated with hunger, which is in a separate part of the fore-brain.

Figure 7.3 Human brain

Study the labelled diagram of the human brain. We have seen that
the different parts have specific functions. Can we find out the function
of each part?
Let us look at the other use of the word ‘reflex’ that we have talked
about in the introduction. Our mouth waters when we see food we like
without our meaning to. Our hearts beat without our thinking about it.
In fact, we cannot control these actions easily by thinking about them
even if we wanted to. Do we have to think about or remember to breathe
or digest food? So, in between the simple reflex actions like change in
the size of the pupil, and the thought out actions such as moving a
chair, there is another set of muscle movements over which we do not
have any thinking control. Many of these involuntary actions are
controlled by the mid-brain and hind-brain. All these involuntary actions
including blood pressure, salivation and vomiting are controlled by the
medulla in the hind-brain.
Think about activities like walking in a straight line, riding a bicycle,
picking up a pencil. These are possible due to a part of the hind-brain
called the cerebellum. It is responsible for precision of voluntary actions
and maintaining the posture and balance of the body. Imagine what
would happen if each of these events failed to take place if we were not
thinking about it.

 Science

2019-20
 
A delicate organ like the brain, which is so important for a variety of
activities, needs to be carefully protected. For this, the body is designed
so that the brain sits inside a bony box. Inside the box, the brain is
contained in a fluid-filled balloon which provides further shock
absorption. If you run your hand down the middle of your back, you
will feel a hard, bumpy structure. This is the vertebral column or
backbone which protects the spinal cord.

 
So far, we have been talking about nervous tissue, and how it collects
information, sends it around the body, processes information, makes
decisions based on information, and conveys decisions to muscles for
action. In other words, when the action or movement is to be performed,
muscle tissue will do the final job. How do animal muscles move? When
a nerve impulse reaches the muscle, the muscle fibre must move. How
does a muscle cell move? The simplest notion of movement at the cellular
level is that muscle cells will move by changing their shape so that they
shorten. So the next question is, how do muscle cells change their shape?
The answer must lie in the chemistry of cellular components. Muscle
cells have special proteins that change both their shape and their
arrangement in the cell in response to nervous electrical impulses. When
this happens, new arrangements of these proteins give the muscle cells
a shorter form. Remember when we talked about muscle tissue in
Class IX, there were different kinds of muscles, such as voluntary muscles
and involuntary muscles. Based on what we have discussed so far, what
do you think the differences between these would be?

        


1. What is the difference between a reflex action and walking?
2. What happens at the synapse between two neurons?
3. Which part of the brain maintains posture and equilibrium of the body?
4. How do we detect the smell of an agarbatti (incense stick)?
5. What is the role of the brain in reflex action?

    


Animals have a nervous system for controlling and coordinating the
activities of the body. But plants have neither a nervous system nor
muscles. So, how do they respond to stimuli? When we touch the leaves
of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa
family), they begin to fold up and droop. When a seed germinates, the
root goes down, the stem comes up into the air. What happens? Firstly,
the leaves of the sensitive plant move very quickly in response to touch.

Control and Coordination 

2019-20
 There is no growth involved in this movement. On the other hand, the
directional movement of a seedling is caused by growth. If it is prevented
from growing, it will not show any movement. So plants show two different
types of movement – one dependent on growth and the other independent
of growth.

 
Let us think about the first kind of movement, such as that of the sensitive
plant. Since no growth is involved, the plant must actually move its leaves
in response to touch. But there is no nervous tissue, nor any muscle
tissue. How does the plant detect the touch, and how do the leaves move
in response?

Figure 7.4 The sensitive plant

If we think about where exactly the plant is touched, and what part
of the plant actually moves, it is apparent that movement happens at a
point different from the point of touch. So, information that a touch has
occurred must be communicated. The plants also use electrical-chemical
means to convey this information from cell to cell, but unlike in animals,
there is no specialised tissue in plants for the conduction of information.
Finally, again as in animals, some cells must change shape in order for
movement to happen. Instead of the specialised proteins found in animal
muscle cells, plant cells change shape by changing the amount of water
in them, resulting in swelling or shrinking, and therefore in changing
shapes.

 
Some plants like the pea plant climb up other plants or fences by means
of tendrils. These tendrils are sensitive to touch. When they come in
contact with any support, the part of the tendril in contact with the object
does not grow as rapidly as the part of the tendril away from the object.
This causes the tendril to circle around the object and thus cling to it.
More commonly, plants respond to stimuli slowly by growing in a
particular direction. Because this growth is directional, it appears as if
the plant is moving. Let us understand this type of movement with the
help of an example.

 Science

2019-20
  
 Fill a conical flask with water.
 Cover the neck of the flask with a wire mesh.
 Keep two or three freshly germinated bean
seeds on the wire mesh.
 Take a cardboard box which is open from one
side.
 Keep the flask in the box in such a manner
that the open side of the box faces light coming
from a window (Fig. 7.5).
 After two or three days, you will notice that
the shoots bend towards light and roots away
from light.
 Now turn the flask so that the shoots are away Figure 7.5
from light and the roots towards light. Leave it Response of the plant to the direction of light
undisturbed in this condition for a few days.
 Have the old parts of the shoot and root
changed direction?
 Are there differences in the direction of the new
growth?
 What can we conclude from this activity?

Environmental triggers such as light, or gravity

will change the directions that plant parts grow in.
These directional, or tropic, movements can be either
towards the stimulus, or away from it. So, in two
different kinds of phototropic movement, shoots
respond by bending towards light while roots
respond by bending away from it. How does this help Figure 7.6 Plant showing geotropism
the plant?
Plants show tropism in response to other stimuli as well. The roots
of a plant always grow downwards while the shoots usually grow
upwards and away from the earth. This upward and downward growth
of shoots and roots, respectively, in response to the pull of earth or gravity
is, obviously, geotropism (Fig. 7.6). If ‘hydro’ means water and ‘chemo’
refers to chemicals, what would ‘hydrotropism’ and ‘chemotropism’
mean? Can we think of examples of these kinds of directional growth
movements? One example of chemotropism is the growth of pollen tubes
towards ovules, about which we will learn more when we examine the
reproductive processes of living organisms.
Let us now once again think about how information is communicated
in the bodies of multicellular organisms. The movement of the
sensitive plant in response to touch is very quick. The movement of
sunflowers in response to day or night, on the other hand, is quite slow.
Growth-related movement of plants will be even slower.
Even in animal bodies, there are carefully controlled directions to
growth. Our arms and fingers grow in certain directions, not haphazardly.
So controlled movements can be either slow or fast. If fast responses to
stimuli are to be made, information transfer must happen very quickly.
For this, the medium of transmission must be able to move rapidly.

Control and Coordination 

2019-20
 Electrical impulses are an excellent means for this. But there are
limitations to the use of electrical impulses. Firstly, they will reach only
those cells that are connected by nervous tissue, not each and every cell
in the animal body. Secondly, once an electrical impulse is generated in
a cell and transmitted, the cell will take some time to reset its mechanisms
before it can generate and transmit a new impulse. In other words, cells
cannot continually create and transmit electrical impulses. It is thus no
wonder that most multicellular organisms use another means of
communication between cells, namely, chemical communication.
If, instead of generating an electrical impulse, stimulated cells release
a chemical compound, this compound would diffuse all around the
original cell. If other cells around have the means to detect this compound
using special molecules on their surfaces, then they would be able to
recognise information, and even transmit it. This will be slower, of course,
but it can potentially reach all cells of the body, regardless of nervous
connections, and it can be done steadily and persistently. These
compounds, or hormones used by multicellular organisms for control
and coordination show a great deal of diversity, as we would expect.
Different plant hormones help to coordinate growth, development and
responses to the environment. They are synthesised at places away from
where they act and simply diffuse to the area of action.
Let us take an example that we have worked with earlier [Activity 7.2].
When growing plants detect light, a hormone called auxin, synthesised
at the shoot tip, helps the cells to grow longer. When light is coming from
one side of the plant, auxin diffuses towards the shady side of the shoot.
This concentration of auxin stimulates the cells to grow longer on the
side of the shoot which is away from light. Thus, the plant appears to
bend towards light.
Another example of plant hormones are gibberellins which, like
auxins, help in the growth of the stem. Cytokinins promote cell division,
and it is natural then that they are present in greater concentration in
areas of rapid cell division, such as in fruits and seeds. These are examples
of plant hormones that help in promoting growth. But plants also need
signals to stop growing. Abscisic acid is one example of a hormone which
inhibits growth. Its effects include wilting of leaves.

        


1. What are plant hormones?
2. How is the movement of leaves of the sensitive plant different from the
movement of a shoot towards light?
3. Give an example of a plant hormone that promotes growth.
4. How do auxins promote the growth of a tendril around a support?
5. Design an experiment to demonstrate hydrotropism.

 Science

2019-20
   
How are such chemical, or hormonal, means of information transmission
used in animals? What do some animals, for instance squirrels,
experience when they are in a scary situation? Their bodies have to
prepare for either fighting or running away. Both are very complicated
activities that will use a great deal of energy in controlled ways. Many
different tissue types will be used and their activities integrated together
in these actions. However, the two alternate activities, fighting or running,
are also quite different! So here is a situation in which some common
preparations can be usefully made in the body. These preparations
should ideally make it easier to do either activity in the near future. How
would this be achieved?
If the body design in the squirrel relied only on electrical impulses
via nerve cells, the range of tissues instructed to prepare for the coming
activity would be limited. On the other hand, if a chemical signal were to
be sent as well, it would reach all cells of the body and provide the wide-
ranging changes needed. This is done in many animals, including human
beings, using a hormone called adrenaline that is secreted from the
adrenal glands. Look at Fig. 7.7 to locate these glands.
Adrenaline is secreted directly into the blood and carried to different
parts of the body. The target organs or the specific tissues on which it
acts include the heart. As a result, the heart beats faster, resulting in
supply of more oxygen to our muscles. The blood to the digestive system
and skin is reduced due to contraction of muscles around small arteries
in these organs. This diverts the blood to our skeletal muscles. The
breathing rate also increases because of the contractions of the
diaphragm and the rib muscles. All these responses together enable the
animal body to be ready to deal with the situation. Such animal hormones
are part of the endocrine system which constitutes a second way of control
and coordination in our body.

 
 Look at Fig. 7.7.
 Identify the endocrine glands mentioned in the figure.
 Some of these glands have been listed in Table 7.1 and discussed
in the text. Consult books in the library and discuss with your
teachers to find out about other glands.

Remember that plants have hormones that control their directional

growth. What functions do animal hormones perform? On the face of it,
we cannot imagine their role in directional growth. We have never seen
an animal growing more in one direction or the other, depending on
light or gravity! But if we think about it a bit more, it will become evident
that, even in animal bodies, growth happens in carefully controlled places.
Plants will grow leaves in many places on the plant body, for example.
But we do not grow fingers on our faces. The design of the body is carefully
maintained even during the growth of children.

Control and Coordination 

2019-20
 (a) (b)

Figure 7.7 Endocrine glands in human beings (a) male, (b) female

Let us examine some examples to understand how hormones help

in coordinated growth. We have all seen salt packets which say ‘iodised
salt’ or ‘enriched with iodine’. Why is it important for us to have iodised
salt in our diet? Iodine is necessary for the thyroid gland to make
 thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat
metabolism in the body so as to provide the best balance for growth.
Hypothalamus plays Iodine is essential for the synthesis of thyroxin. In case iodine is deficient
an important role in in our diet, there is a possibility that we might suffer from goitre. One
the release of many of the symptoms in this disease is a swollen neck. Can you correlate
hormones. For this with the position of the thyroid gland in Fig. 7.7?
example, when the Sometimes we come across people who are either very short (dwarfs)
level of growth or extremely tall (giants). Have you ever wondered how this happens?
hormone is low, the Growth hormone is one of the hormones secreted by the pituitary. As
hypothalamus its name indicates, growth hormone regulates growth and development
releases growth of the body. If there is a deficiency of this hormone in childhood, it
hormone releasing leads to dwarfism.
factor which You must have noticed many dramatic changes in your appearance
stimulates the as well as that of your friends as you approached 10–12 years of age.
pituitary gland to These changes associated with puberty are because of the secretion of
release growth testosterone in males and oestrogen in females.
hormone. Do you know anyone in your family or friends who has been advised
by the doctor to take less sugar in their diet because they are suffering
from diabetes? As a treatment, they might be taking injections of insulin.
This is a hormone which is produced by the pancreas and helps in
regulating blood sugar levels. If it is not secreted in proper amounts,
the sugar level in the blood rises causing many harmful effects.

 Science

2019-20
 If it is so important that hormones should be secreted in precise
quantities, we need a mechanism through which this is done. The timing
and amount of hormone released are regulated by feedback mechanisms.
For example, if the sugar levels in blood rise, they are detected by the
cells of the pancreas which respond by producing more insulin. As the
blood sugar level falls, insulin secretion is reduced.

 
 Hormones are secreted by endocrine glands and have specific functions. Complete
Table 7.1 based on the hormone, the endocrine gland or the functions provided.

Table 7.1 : Some important hormones and their functions

S.No. Hormone Endocrine Gland Functions

1. Growth hormone Pituitary gland Stimulates growth in all organs

2. Thyroid gland Regulates metabolism for body growth
3. Insulin Regulates blood sugar level
4. Testosterone Testes
5. Ovaries Development of female sex organs,
regulates menstrual cycle, etc.
6. Adrenaline Adrenal gland
7. Releasing Stimulates pituitary gland to release
hormones hormones

        


1. How does chemical coordination take place in animals?
2. Why is the use of iodised salt advisable?
3. How does our body respond when adrenaline is secreted into the blood?
4. Why are some patients of diabetes treated by giving injections of insulin?


 Control and coordination are the functions of the nervous system and hormones
in our bodies.
 The responses of the nervous system can be classified as reflex action, voluntary
action or involuntary action.
 The nervous system uses electrical impulses to transmit messages.
 The nervous system gets information from our sense organs and acts through our
muscles.
 Chemical coordination is seen in both plants and animals.
 Hormones produced in one part of an organism move to another part to achieve
the desired effect.
 A feedback mechanism regulates the action of the hormones.

Control and Coordination 

2019-20
         
1. Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin.
2. The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
3. The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
4. What is the function of receptors in our body? Think of situations where receptors
do not work properly. What problems are likely to arise?
5. Draw the structure of a neuron and explain its function.
6. How does phototropism occur in plants?
7. Which signals will get disrupted in case of a spinal cord injury?
8. How does chemical coordination occur in plants?
9. What is the need for a system of control and coordination in an organism?
10. How are involuntary actions and reflex actions different from each other?
11. Compare and contrast nervous and hormonal mechanisms for control and
coordination in animals.
12. What is the difference between the manner in which movement takes place in a
sensitive plant and the movement in our legs?

 Science

2019-20
  

?

B efore we discuss the mechanisms by which organisms reproduce,

let us ask a more basic question – why do organisms reproduce?
After all, reproduction is not necessary to maintain the life of an individual
organism, unlike the essential life processes such as nutrition,
respiration, or excretion. On the other hand, if an individual organism is
going to create more individuals, a lot of its energy will be spent in the
process. So why should an individual organism waste energy on a process
it does not need to stay alive? It would be interesting to discuss the
possible answers in the classroom!
Whatever the answer to this question, it is obvious that we notice
organisms because they reproduce. If there were to be only one, non-
reproducing member of a particular kind, it is doubtful that we would
have noticed its existence. It is the large numbers of organisms belonging
to a single species that bring them to our notice. How do we know that
two different individual organisms belong to the same species? Usually,
we say this because they look similar to each other. Thus, reproducing
organisms create new individuals that look very much like themselves.

    

  
   

 

Organisms look similar because their body designs are similar. If body
designs are to be similar, the blueprints for these designs should be
similar. Thus, reproduction at its most basic level will involve making
copies of the blueprints of body design. In Class IX, we learnt that the
chromosomes in the nucleus of a cell contain information for inheritance
of features from parents to next generation in the form of DNA (Deoxyribo
Nucleic Acid) molecules. The DNA in the cell nucleus is the information
source for making proteins. If the information is changed, different
proteins will be made. Different proteins will eventually lead to altered
body designs.
Therefore, a basic event in reproduction is the creation of a DNA
copy. Cells use chemical reactions to build copies of their DNA. This
creates two copies of the DNA in a reproducing cell, and they will need to
be separated from each other. However, keeping one copy of DNA in the
original cell and simply pushing the other one out would not work,

2019-20
 because the copy pushed out would not have any organised cellular
structure for maintaining life processes. Therefore, DNA copying is
accompanied by the creation of an additional cellular apparatus, and
then the DNA copies separate, each with its own cellular apparatus.
Effectively, a cell divides to give rise to two cells.
These two cells are of course similar, but are they likely to be
absolutely identical? The answer to this question will depend on how
accurately the copying reactions involved occur. No bio-chemical reaction
is absolutely reliable. Therefore, it is only to be expected that the process
of copying the DNA will have some variations each time. As a result, the
DNA copies generated will be similar, but may not be identical to the
original. Some of these variations might be so drastic that the new DNA
copy cannot work with the cellular apparatus it inherits. Such a newborn
cell will simply die. On the other hand, there could still be many other
variations in the DNA copies that would not lead to such a drastic
outcome. Thus, the surviving cells are similar to, but subtly different
from each other. This inbuilt tendency for variation during reproduction
is the basis for evolution, as we will discuss in the next chapter.


Populations of organisms fill well-defined places, or niches, in the
ecosystem, using their ability to reproduce. The consistency of DNA
copying during reproduction is important for the maintenance of body
design features that allow the organism to use that particular niche.
Reproduction is therefore linked to the stability of populations of species.
However, niches can change because of reasons beyond the control
of the organisms. Temperatures on earth can go up or down, water levels
can vary, or there could be meteorite hits, to think of a few examples. If
a population of reproducing organisms were suited to a particular niche
and if the niche were drastically altered, the population could be wiped
out. However, if some variations were to be present in a few individuals
in these populations, there would be some chance for them to survive.
Thus, if there were a population of bacteria living in temperate waters,
and if the water temperature were to be increased by global warming,
most of these bacteria would die, but the few variants resistant to heat
would survive and grow further. Variation is thus useful for the survival
of species over time.

        
1.
2.
What is the importance of DNA copying in reproduction?
Why is variation beneficial to the species but not necessarily
for the individual?

 Science

2019-20
      

 
 Dissolve about 10 gm of sugar in 100 mL of water.
 Take 20 mL of this solution in a test tube and add a pinch of yeast
granules to it.
 Put a cotton plug on the mouth of the test tube and keep it in a
warm place.
 After 1 or 2 hours, put a small drop of yeast culture from the test
tube on a slide and cover it with a coverslip.
 Observe the slide under a microscope.

 
 Wet a slice of bread, and keep it in a cool, moist and dark place.
 Observe the surface of the slice with a magnifying glass.
 Record your observations for a week.

Compare and contrast the ways in which yeast grows in the first
case, and how mould grows in the second.
Having discussed the context in which reproductive processes work,
let us now examine how different organisms actually reproduce. The
modes by which various organisms reproduce depend on the body
design of the organisms.

 
For unicellular organisms, cell division, or fission, leads to the creation
of new individuals. Many different patterns of fission have been observed.
Many bacteria and protozoa simply split into two equal halves during
cell division. In organisms such as Amoeba, the splitting of the two cells
during division can take place in any plane.

 
 Observe a permanent slide of
Amoeba under a microscope.
 Similarly observe another Figure 8.1(a) Binary fission in Amoeba
permanent slide of Amoeba
showing binary fission.
 Now, compare the observations of
both the slides.

However, some unicellular organisms

show somewhat more organisation of their
bodies, such as is seen in Leishmania (which
(a) (b) (c) (d) (e) (f)
cause kala-azar), which have a whip-like
Figure 8.1(b) Binary fission in Leishmania
structure at one end of the cell. In such
organisms, binary fission occurs in a definite orientation in relation to

How do Organisms Reproduce? 

2019-20
 these structures. Other single-celled organisms, such as the malarial
parasite, Plasmodium, divide into many daughter cells simultaneously
by multiple fission.
Yeast, on the other hand, can put out small buds that separate and
grow further, as we saw in Activity 8.1.


Figure 8.2
Multiple fission in
Plasmodium  
 Collect water from a lake or pond that appears dark green and
contains filamentous structures.
 Put one or two filaments on a slide.
 Put a drop of glycerine on these filaments and cover it with a coverslip.
 Observe the slide under a microscope.
 Can you identify different tissues in the Spirogyra filaments?

In multi-cellular organisms with relatively simple body organisation,

simple reproductive methods can still work. Spirogyra, for example,
simply breaks up into smaller pieces upon maturation. These pieces or
fragments grow into new individuals. Can we work out the reason for
this, based on what we saw in Activity 8.4?
This is not true for all multi-cellular organisms. They cannot simply
divide cell-by-cell. The reason is that many multi-cellular organisms, as
we have seen, are not simply a random collection of cells. Specialised
cells are organised as tissues, and tissues are organised into organs,
which then have to be placed at definite positions in the body. In such a
carefully organised situation, cell-by-cell division would be impractical.
Multi-cellular organisms, therefore, need to use more complex ways of
reproduction.
A basic strategy used in multi-cellular organisms is that different
cell types perform different specialised functions. Following this general
pattern, reproduction in such organisms is also the function of a specific
cell type. How is reproduction to be achieved from a single cell type, if
the organism itself consists of many cell types? The answer is that there
must be a single cell type in the organism that is capable of growing,
proliferating and making other cell types under the right circumstances.


Many fully differentiated organisms have the ability to give rise to new
individual organisms from their body parts. That is, if the individual is
somehow cut or broken up into many pieces, many of these pieces grow
into separate individuals. For example, simple animals like Hydra and
Planaria can be cut into any number of pieces and each piece grows
into a complete organism. This is known as regeneration (see Fig. 8.3).
Regeneration is carried out by specialised cells. These cells proliferate
and make large numbers of cells. From this mass of cells, different cells
undergo changes to become various cell types and tissues. These changes

 Science

2019-20
 take place in an organised
sequence referred to as
development. However,
regeneration is not the same
as reproduction, since most
organisms would not
normally depend on being cut
up to be able to reproduce.

 
Organisms such as Hydra
use regenerative cells for
reproduction in the process of
budding. In Hydra, a bud
Figure 8.3 Regeneration in Planaria develops as an outgrowth due
to repeated cell division at one
specific site (Fig. 8.4). These buds develop into tiny individuals and when
fully mature, detach from the parent body and become new independent
individuals.

Figure 8.4 Budding in Hydra


There are many plants in which parts like the root, stem and leaves
develop into new plants under appropriate conditions. Unlike in most
animals, plants can indeed use such a mode for reproduction. This
property of vegetative propagation is used in methods such as layering
or grafting to grow many plants like sugarcane, roses, or grapes for
agricultural purposes. Plants raised by vegetative propagation can bear
flowers and fruits earlier than those produced from seeds. Such methods
also make possible the propagation of plants such as banana, orange,
rose and jasmine that have lost the capacity to produce seeds. Another
advantage of vegetative propagation is that all plants produced are
genetically similar enough to the parent plant to have all its
characteristics.

How do Organisms Reproduce? 

2019-20
  
 Take a potato and observe its surface. Can notches be seen?
 Cut the potato into small pieces such that some pieces contain a
notch or bud and some do not.
 Spread some cotton on a tray and wet it. Place the potato pieces
on this cotton. Note where the pieces with the buds are placed.
 Observe changes taking place in these potato pieces over the next
few days. Make sure that the cotton is kept moistened.
 Which are the potato pieces that give rise to fresh green shoots
and roots?

Similarly buds produced in the notches along the leaf

margin of Bryophyllum fall on the soil and develop into
new plants (Fig. 8.5).

 
 Select a money-plant.
 Cut some pieces such that they contain at least
Figure 8.5 one leaf.
Leaf of Bryophyllum  Cut out some other portions between two leaves.
with buds  Dip one end of all the pieces in water and observe
over the next few days.
 Which ones grow and give rise to fresh leaves?
 What can you conclude from your observations?


Tissue culture
In tissue culture, new plants are grown by removing tissue or separating cells from
the growing tip of a plant. The cells are then placed in an artificial medium where they
divide rapidly to form a small group of cells or callus. The callus is transferred to
another medium containing hormones for growth and differentiation. The plantlets
are then placed in the soil so that they can grow into mature plants. Using tissue
culture, many plants can be grown from one parent in disease-free conditions. This
technique is commonly used for ornamental plants.


Even in many simple multi-cellular organisms, specific reproductive
parts can be identified. The thread-like structures that developed on
the bread in Activity 8.2 above are the hyphae of the bread mould
(Rhizopus). They are not reproductive parts. On the other hand, the
tiny blob-on-a-stick structures are involved in reproduction. The
blobs are sporangia, which contain cells, or spores, that can
eventually develop into new Rhizopus individuals (Fig. 8.6). The spores
Figure 8.6 are covered by thick walls that protect them until they come into
Spore formation in Rhizopus contact with another moist surface and can begin to grow.

 Science

2019-20
 All the modes of reproduction that we have discussed so far allow
new generations to be created from a single individual. This is known as
asexual reproduction.

        


1. How does binary fission differ from multiple fission?
2. How will an organism be benefited if it reproduces through spores?
3. Can you think of reasons why more complex organisms cannot give
rise to new individuals through regeneration?
4. Why is vegetative propagation practised for growing some types of
plants?
5. Why is DNA copying an essential part of the process of reproduction?

  

We are also familiar with modes of reproduction that depend on the
involvement of two individuals before a new generation can be created.
Bulls alone cannot produce new calves, nor can hens alone produce
new chicks. In such cases, both sexes, males and females, are needed to
produce new generations. What is the significance of this sexual mode
of reproduction? Are there any limitations of the asexual mode of
reproduction, which we have been discussing above?


The creation of two new cells from one involves copying of the DNA as
well as of the cellular apparatus. The DNA copying mechanism, as we
have noted, cannot be absolutely accurate, and the resultant errors are
a source of variations in populations of organisms. Every individual
organism cannot be protected by variations, but in a population,
variations are useful for ensuring the survival of the species. It would
therefore make sense if organisms came up with reproductive modes
that allowed more and more variation to be generated.
While DNA-copying mechanisms are not absolutely accurate, they
are precise enough to make the generation of variation a fairly slow
process. If the DNA copying mechanisms were to be less accurate, many
of the resultant DNA copies would not be able to work with the cellular
apparatus, and would die. So how can the process of making variants
be speeded up? Each new variation is made in a DNA copy that already
has variations accumulated from previous generations. Thus, two
different individuals in a population would have quite different patterns
of accumulated variations. Since all of these variations are in living
individuals, it is assured that they do not have any really bad effects.
Combining variations from two or more individuals would thus create
new combinations of variants. Each combination would be novel, since
it would involve two different individuals. The sexual mode of

How do Organisms Reproduce? 

2019-20
 reproduction incorporates such a process of combining DNA from two
different individuals during reproduction.
But this creates a major difficulty. If each new generation is to be the
combination of the DNA copies from two pre-existing individuals, then
each new generation will end up having twice the amount of DNA that
the previous generation had. This is likely to mess up the control of the
cellular apparatus by the DNA. How many ways can we think of for
solving this difficulty?
We have seen earlier that as organisms become more complex, the
specialisation of tissue increases. One solution that many multi-cellular
organisms have found for the problem mentioned above is to have special
lineages of cells in specialised organs in which only half the number of
chromosomes and half the amount of DNA as compared to the non-
reproductive body cells. This is achieved by a process of cell division
called meiosis. Thus, when these germ-cells from two individuals combine
during sexual reproduction to form a new individual, it results in re-
establishment of the number of chromosomes and the DNA content in
the new generation.
If the zygote is to grow and develop into an organism which has
highly specialised tissues and organs, then it has to have sufficient stores
of energy for doing this. In very simple organisms, it is seen that the two
germ-cells are not very different from one another, or may even be similar.
But as the body designs become more complex, the germ-cells also
specialise. One germ-cell is large and contains the food-stores while the
other is smaller and likely to be motile. Conventionally, the motile germ-
cell is called the male gamete and the germ-cell containing the stored
food is called the female gamete. We shall see in the next few sections
how the need to create these two different types of gametes give rise to
differences in the male and female reproductive organs and, in some
cases, differences in the bodies of the male and female organisms.


The reproductive parts of angiosperms are located in the flower. You
have already studied the different parts of a flower – sepals, petals,
stamens and pistil. Stamens and pistil are
the reproductive parts of a flower which
contain the germ-cells. What possible
functions could the petals and sepals serve?
The flower may be unisexual (papaya,
watermelon) when it contains either stamens
or pistil or bisexual (Hibiscus, mustard)
when it contains both stamens and pistil.
Stamen is the male reproductive part and it
produces pollen grains that are yellowish
in colour. You must have seen this yellowish
powder that often sticks to our hands if we
Figure 8.7 touch the stamen of a flower. Pistil is present
Longitudinal section of in the centre of a flower and is the female
flower reproductive part. It is made of three parts.

 Science

2019-20
The swollen bottom part is the ovary, middle elongated part is the style
and the terminal part which may be sticky is the stigma. The ovary
contains ovules and each ovule has an egg cell. The male germ-cell
produced by pollen grain fuses with the female gamete present in
the ovule. This fusion of the germ-cells or fertilisation gives us the
zygote which is capable of growing into a new plant.
Thus the pollen needs to be transferred from the stamen to the
stigma. If this transfer of pollen occurs in the same flower, it is
referred to as self-pollination. On the other hand, if the pollen is
transferred from one flower to another, it is known as cross-
pollination. This transfer of pollen from one flower to another is
achieved by agents like wind, water or animals.
After the pollen lands on a suitable stigma, it has to reach the
female germ-cells which are in the ovary. For this, a tube grows
out of the pollen grain and travels through the style to reach the
ovary.
After fertilisation, the zygote divides several times to form an
embryo within the ovule. The ovule develops a tough coat and is
gradually converted into a seed. The ovary grows rapidly and ripens
to form a fruit. Meanwhile, the petals, sepals, stamens, style and
stigma may shrivel and fall off. Have you ever observed any flower
part still persisting in the fruit? Try and work out the advantages Figure 8.8
Germination of pollen on
of seed-formation for the plant. The seed contains the future plant
stigma
or embryo which develops into a seedling under appropriate
conditions. This process is known as germination.

 
 Soak a few seeds of Bengal gram (chana)
and keep them overnight.
 Drain the excess water and cover the seeds
with a wet cloth and leave them for a day. Figure 8.9
Make sure that the seeds do not become dry. Germination
 Cut open the seeds carefully and observe
the different parts.
 Compare your observations with the Fig. 8.9
and see if you can identify all the parts.


So far, we have been discussing the variety of modes that different species
use for reproduction. Let us now look at the species that we are most
interested in, namely, humans. Humans use a sexual mode of
reproduction. How does this process work?
Let us begin at an apparently unrelated point. All of us know that
our bodies change as we become older. You have learnt changes that
take place in your body earlier in Class VIII also. We notice that our
height has increased continuously from early age till now. We acquire
teeth, we even lose the old, so-called milk teeth and acquire new ones.

How do Organisms Reproduce? 

2019-20
 All of these are changes that can be grouped under the general process
of growth, in which the body becomes larger. But in early teenage years,
a whole new set of changes occurs that cannot be explained simply as
body enlargement. Instead, the appearance of the body changes.
Proportions change, new features appear, and so do new sensations.
Some of these changes are common to both boys and girls. We begin
to notice thick hair growing in new parts of the body such as armpits
and the genital area between the thighs, which can also become darker
in colour. Thinner hair can also appear on legs and arms, as well as on
the face. The skin frequently becomes oily and we might begin to develop
pimples. We begin to be conscious and aware of both our own bodies
and those of others in new ways.
On the other hand, there are also changes taking place that are
different between boys and girls. In girls, breast size begins to increase,
with darkening of the skin of the nipples at the tips of the breasts. Also,
girls begin to menstruate at around this time. Boys begin to have new
thick hair growth on the face and their voices begin to crack. Further,
the penis occasionally begins to become enlarged and erect, either in
daydreams or at night.
All of these changes take place slowly, over a period of months and
years. They do not happen all at the same time in one person, nor do
they happen at an exact age. In some people, they happen early and
quickly, while in others, they can happen slowly. Also, each change does
not become complete quickly either. So, for example, thick hair on the
face in boys appears as a few scattered hairs first, and only slowly does
the growth begin to become uniform. Even so, all these changes show
differences between people. Just as we have differently shaped noses or
fingers, so also we have different patterns of hair growth, or size and
shape of breast or penis. All of these changes are aspects of the sexual
maturation of the body.
Why does the body show sexual maturation at this age? We have
talked about the need for specialised cell types in multi-cellular bodies
to carry out specialised functions. The creation of germ-cells to participate
in sexual reproduction is another specialised function, and we have seen
that plants develop special cell and tissue types to create them. Human
beings also develop special tissues for this purpose. However, while the
body of the individual organism is growing to its adult size, the resources
of the body are mainly directed at achieving this growth. While that is
happening, the maturation of the reproductive tissue is not likely to be
a major priority. Thus, as the rate of general body growth begins to slow
down, reproductive tissues begin to mature. This period during
adolescence is called puberty.
So how do all the changes that we have talked about link to the
reproductive process? We must remember that the sexual mode of
reproduction means that germ-cells from two individuals have to join
together. This can happen by the external release of germ-cells from the
bodies of individuals, as happens in flowering plants. Or it can happen
by two individuals joining their bodies together for internal transfer of
germ-cells for fusion, as happens in many animals. If animals are to

 Science

2019-20
participate in this process of mating, their state of sexual maturity must
be identifiable by other individuals. Many changes during puberty, such
as new hair-growth patterns, are signals that sexual maturation is taking
place.
On the other hand, the actual transfer of germ-cells between two
people needs special organs for the sexual act, such as the penis when it
is capable of becoming erect. In mammals such as humans, the baby is
carried in the mother’s body for a long period, and will be breast-fed
later. The female reproductive organs and breasts will need to mature to
accommodate these possibilities. Let us look at the systems involved in
the process of sexual reproduction.


The male reproductive system (Fig. 8.10)
consists of portions which produce the
germ-cells and other portions that deliver
the germ-cells to the site of fertilisation.
The formation of germ-cells or sperms
takes place in the testes. These are located
outside the abdominal cavity in scrotum
because sperm formation requires a lower
temperature than the normal body
temperature. We have discussed the role of the
testes in the secretion of the hormone,
testosterone, in the previous chapter. In
addition to regulating the formation of sperms,
testosterone brings about changes in
appearance seen in boys at the time of puberty.
The sperms formed are delivered
through the vas deferens which unites with Figure 8.10 Human –male reproductive system
a tube coming from the urinary bladder. The
urethra thus forms a common passage for
both the sperms and urine. Along the path
of the vas deferens, glands like the prostate
and the seminal vesicles add their secretions
so that the sperms are now in a fluid which
makes their transport easier and this fluid
also provides nutrition. The sperms are tiny
bodies that consist of mainly genetic
material and a long tail that helps them to
move towards the female germ-cell.


The female germ-cells or eggs are made in
the ovaries. They are also responsible for the
production of some hormones. Look at
Fig. 8.11 and identify the various organs in
the female reproductive system. Figure 8.11 Human –female reproductive system

How do Organisms Reproduce? 

2019-20
 When a girl is born, the ovaries already contain thousands of
immature eggs. On reaching puberty, some of these start maturing. One
egg is produced every month by one of the ovaries. The egg is carried
from the ovary to the womb through a thin oviduct or fallopian tube.
The two oviducts unite into an elastic bag-like structure known as the
uterus. The uterus opens into the vagina through the cervix.
The sperms enter through the vaginal passage during sexual
intercourse. They travel upwards and reach the oviduct where they may
encounter the egg. The fertilised egg (zygote) starts dividing and form a
ball of cells or embryo. The embryo is implanted in the lining of the uterus
where they continue to grow and develop organs to become foetus. We
have seen in earlier sections that the mother’s body is designed to
undertake the development of the child. Hence the uterus prepares itself
every month to receive and nurture the growing embryo. The lining
thickens and is richly supplied with blood to nourish the growing embryo.
The embryo gets nutrition from the mother’s blood with the help of a
special tissue called placenta. This is a disc which is embedded in the
uterine wall. It contains villi on the embryo’s side of the tissue. On the
mother’s side are blood spaces, which surround the villi. This provides
a large surface area for glucose and oxygen to pass from the mother to
the embryo. The developing embryo will also generate waste substances
which can be removed by transferring them into the mother’s blood
through the placenta. The development of the child inside the mother’s
body takes approximately nine months. The child is born as a result of
rhythmic contractions of the muscles in the uterus.


If the egg is not fertilised, it lives for about one day. Since the ovary
releases one egg every month, the uterus also prepares itself every month
to receive a fertilised egg. Thus its lining becomes thick and spongy.
This would be required for nourishing the embryo if fertilisation had
taken place. Now, however, this lining is not needed any longer. So, the
lining slowly breaks and comes out through the vagina as blood and
mucous. This cycle takes place roughly every month and is known as
menstruation. It usually lasts for about two to eight days.


As we have seen, the process of sexual maturation is gradual, and takes
place while general body growth is still going on. Therefore, some degree
of sexual maturation does not necessarily mean that the body or the
mind is ready for sexual acts or for having and bringing up children.
How do we decide if the body or the mind is ready for this major
responsibility? All of us are under many different kinds of pressures
about these issues. There can be pressure from our friends for
participating in many activities, whether we really want to or not. There
can be pressure from families to get married and start having children.
There can be pressure from government agencies to avoid having
children. In this situation, making choices can become very difficult.

 Science

2019-20
 We must also consider the possible health consequences of having
sex. We have discussed in Class IX that diseases can be transmitted
from person to person in a variety of ways. Since the sexual act is a
very intimate connection of bodies, it is not surprising that many
diseases can be sexually transmitted. These include bacterial infections
such as gonorrhoea and syphilis, and viral infections such as warts
and HIV-AIDS. Is it possible to prevent the transmission of such diseases
during the sexual act? Using a covering, called a condom, for the penis
during sex helps to prevent transmission of many of these infections to
some extent.
The sexual act always has the potential to lead to pregnancy.
Pregnancy will make major demands on the body and the mind of the
woman, and if she is not ready for it, her health will be adversely
affected. Therefore, many ways have been devised to avoid pregnancy.
These contraceptive methods fall in a number of categories. One
category is the creation of a mechanical barrier so that sperm does not
reach the egg. Condoms on the penis or similar coverings worn in the
vagina can serve this purpose. Another category of contraceptives acts
by changing the hormonal balance of the body so that eggs are not
released and fertilisation cannot occur. These drugs commonly need
to be taken orally as pills. However, since they change hormonal
balances, they can cause side-effects too. Other contraceptive devices
such as the loop or the copper-T are placed in the uterus to prevent
pregnancy. Again, they can cause side effects due to irritation of the
uterus. If the vas deferens in the male is blocked, sperm transfer will
be prevented. If the fallopian tube in the female is blocked, the egg will
not be able to reach the uterus. In both cases fertilisation will not take
place. Surgical methods can be used to create such blocks. While
surgical methods are safe in the long run, surgery itself can cause
infections and other problems if not performed properly. Surgery can
also be used for removal of unwanted pregnancies. These may be
misused by people who do not want a particular child, as happens in
illegal sex-selective abortion of female foetuses. For a healthy society,
the female-male sex ratio must be maintained. Because of reckless
female foeticides, child sex ratio is declining at an alarming rate in
some sections of our society, although prenatal sex determination has
been prohibited by law.
We have noted earlier that reproduction is the process by which
organisms increase their populations. The rates of birth and death in a
given population will determine its size. The size of the human population
is a cause for concern for many people. This is because an expanding
population makes it harder to improve everybody’s standard of living.
However, if inequality in society is the main reason for poor standards of
living for many people, the size of the population is relatively unimportant.
If we look around us, what can we identify as the most important
reason(s) for poor living standards?

How do Organisms Reproduce? 

2019-20
         


1. How is the process of pollination different from fertilisation?
2. What is the role of the seminal vesicles and the prostate gland?
3. What are the changes seen in girls at the time of puberty?
4. How does the embryo get nourishment inside the mother’s body?
5. If a woman is using a copper -T, will it help in protecting her from
sexually transmitted diseases?


 Reproduction, unlike other life processes, is not essential to maintain the life of an
individual organism.
 Reproduction involves creation of a DNA copy and additional cellular apparatus
by the cell involved in the process.
 Various organisms use different modes of reproduction depending on their body
design.
 In fission, many bacteria and protozoa simply divide into two or more daughter
cells.
 Organisms such as hydra can regenerate if they are broken into pieces. They can
also give out buds which mature into new individuals.
 Roots, stems and leaves of some plants develop into new plants through vegetative
propagation.
 These are examples of asexual reproduction where new generations are created
from a single individual.
 Sexual reproduction involves two individuals for the creation of a new individual.
 DNA copying mechanisms creates variations which are useful for ensuring the
survival of the species. Modes of sexual reproduction allow for greater variation to
be generated.
 Reproduction in flowering plants involves transfer of pollen grains from the anther
to the stigma which is referred to as pollination. This is followed by fertilisation.
 Changes in the body at puberty, such as increase in breast size in girls and new
facial hair growth in boys, are signs of sexual maturation.
 The male reproductive system in human beings consists of testes which produce
sperms, vas deferens, seminal vesicles, prostate gland, urethra and penis.
 The female reproductive system in human beings consists of ovaries, fallopian
tubes, uterus and vagina.
 Sexual reproduction in human beings involves the introduction of sperm in the
vagina of the female. Fertilisation occurs in the fallopian tube.
 Contraception to avoid pregnancy can be achieved by the use of condoms, oral
pills, copper-T and other methods.

 Science

2019-20
         
1. Asexual reproduction takes place through budding in
(a) amoeba.
(b) yeast.
(c) plasmodium.
(d) leishmania.
2. Which of the following is not a part of the female reproductive system in human
beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
3. The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
4. What are the advantages of sexual reproduction over asexual reproduction?
5. What are the functions performed by the testis in human beings?
6. Why does menstruation occur?
7. Draw a labelled diagram of the longitudinal section of a flower.
8. What are the different methods of contraception?
9. How are the modes for reproduction different in unicellular and
multicellular organisms?
10. How does reproduction help in providing stability to populations of species?
11. What could be the reasons for adopting contraceptive methods?

How do Organisms Reproduce? 

2019-20