 KS3

Cells and Reproduction

Part of ScienceBiology
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1. Cells
2. Animal cells and plant cells
3. Cells and their functions
4. Specialised cells
5. Unicellular organisms
6. Reproduction
7. The male reproductive system
8. The female reproductive system
9. Puberty
10.Plant reproduction
1. Pollination
2. Germination
Life processes

The proper name for a living thing is a living organism. A living organism can
be, amongst other things, a plant or an animal. But how can we tell the difference
between something that is living, or dead, or has never been living?To be
classified as living there are seven things an organism must show:
The phrase MRS GREN is one way to remember them:

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MRS
GREN Definition

Movement all living things move, even plants

Respiration getting energy from food

detecting changes in the

Sensitivity surroundings

Growth all living things grow

Reproducti making more living things of the

on same type

Excretion getting rid of waste

Nutrition taking in and using food

MRS GREN
Sometimes it’s easy to tell if something is living or not. A teddy bear might look
like a bear, but it cannot do any of the seven things it needs to be able to do to
count as being alive.
A car can move, it gets energy from petrol (like nutrition and respiration), it might
have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust
pipe (excretion). But it cannot grow or make baby cars. So, a car is not alive.
Cells
All living organisms are made up of cells. Cells are the building units of life - the
basic building blocks of all animals and plants. They are so small, you need to use
a light microscope to see them.
The light microscope

A light microscope uses a series of lenses to produce a magnified image of an

object:

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  the object is placed on a rectangular glass slide
 the slide is placed on a stage with a light source below
 light shines through the object and into the objective lens
 the light passes through the eyepiece lens and from there into your eye

You can focus the image using one or more focusing knobs. It is safest to focus
by using the knobs to move the stage downwards, rather than upwards. There is
a chance of the objective lens and slide colliding if you focus upwards.
Microscopes often have three or four objective lenses on a turret that you can
turn. It is wise to observe an object using the lowest magnification lens first. You
may need to adjust the focus and the amount of light as you move to higher
magnifications.

Image caption,
Plant cells seen through a light microscope
Making a slide

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Onion cells are easy to see using a light microscope. Here is a typical method for
preparing a slide of onion cells:

 cut open an onion

 use forceps to peel a thin layer from the inside
 spread out the layer on a microscope slide
 add a drop of iodine solution to the layer
 carefully place a cover slip over the layer

Image caption,
Stains like iodine make features such as the nucleus easier to see
Observing cells
When you observe cells, it is usual to make a drawing of what you see. Very often
there is so much to see that you can only aim to draw part of it:

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 use pencil rather than pen or colours
 outline the features as accurately as you can using black lines.
 no shading
 label your drawing with the name of the sample and the total
magnification you used

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Image caption,
Cheek cells stained with methylene blue
Total magnification
The magnification of each lens is shown next to the lens:
Total magnification = eyepiece lens magnification × objective lens magnification
For example, if the eyepiece magnification is ×10 and the objective lens
magnification is ×40:
Total magnification = 10 x 40 = ×400 (400 times)
The microscope is thought to have been invented by a Dutch father-son team of
spectacle makers named Hans and Zacharias Janssen in the 1590s. However, it
wasn’t until the mid-seventeenth century that it was first used to make
discoveries.
In 1665 a scientist called Robert Hooke was using a microscope to look at a thin
slice of cork. He saw lots of little boxes in the cork, and he called these boxes
‘cells’.
Animal cells and plant cells
Animal cells usually have an irregular shape, and plant cells usually have a
regular shape. Cells are made up of different parts.
It is easier to describe these parts by using diagrams:

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Animal cells and plant cells both contain:
 cell membrane
 cytoplasm
 nucleus
 mitochondria
Plant cells also contain these parts, which are not found in animal cells:
 cell wall
 vacuole
 chloroplasts
The table summarises the functions of these parts:

Part Function Found In

Cell Controls the movement of substances into and out of Plant and
membrane the cell animal cells

Jelly-like substance, where chemical reactions take Plant and

Cytoplasm place animal cells

Nucleus Carries genetic information and controls the Plant and

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Part Function Found In

activities of the cell animal cells

Mitochondri Plant and

a Where most respiration reactions happen animal cells

Contains a liquid called cell sap, which keeps the cell

Vacuole firm Plant cells only

Made of a tough substance called cellulose, which

Cell wall supports and strengthens the cell Plant cells only

Absorbs light energy and converts it into chemical Green plant

Chloroplasts energy (food) cells only

Find out from a greengrocer and a butcher how the structure of a particular cell
affects their produce
Activity - Cells

Start activity
Cells quiz
Find out how much you know in this quick science quiz!
Cells and their functions
How to make a model plant cell
Humans are multicellular. That means we are made of lots of cells, not just one
cell.
 Cells are the basic building blocks of all animals and plants
 The same type of cells group together to form a tissue
 When different tissues group together they form an organ
 Organs working together to form organ systems
 Different organ systems work together to form an organism

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The cells in many multicellular animals and plants are specialised, so that they
can share out the processes of life. They work together like a team to support the
different processes in an organism.
Animal cells and plant cells can form tissues, such as muscle tissue in animals. A
living tissue is made from a group of cells with a similar structure and function,
which all work together to do a particular job.
When different tissues group together they form an organ.
An organ system is made from a group of different organs, which all work
together to do a particular job.
An organism is formed when different organ systems work together.
 you are an organism
 the circulatory system is an organ system
 your heart is an organ
 it has muscle tissue,
 muscle tissues are made from muscle cells
Specialised cells
Find out how a sports therapist uses his knowledge of specialised cells to help his
clients
This diagram shows examples of some specialised animal cells. Notice that they
look very different from one another.

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Image caption,
A selection of specialised animal cells
These tables show examples of some specialised animal and plant cells, with
their functions and special features:

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11
Activity - Specialised cells

Start activity
Test your knowledge
Unicellular organisms
A single celled, unicellular organism is a living thing that is just one cell. There
are different types of unicellular organism, including:
 bacteria
 protozoa
 unicellular fungi
 algae
 Archaea
You might be tempted to think that these organisms are very simple, but in fact
they can be very complex. They can carry out all seven life processes -
movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.
They have adaptations that make them very well suited for life in their
environment.
Bacteria

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Bacteria are tiny. A typical bacterial cell is just a few thousandths of a millimetre
across.
The structure of a bacterial cell is different to an animal or plant cell.
Protozoa
Protozoa are single celled organisms that live in water or in damp places. The
amoeba is an example of one.

Image caption,
A light microscope image of an amoeba, showing several pseudopodia (false feet)
Although it is just one cell, it has adaptations that let it behave a bit like an
animal:
 it produces pseudopodia (“false feet”) that let it move about
 its pseudopodia can surround food and take it inside the cell
 contractile vacuoles appear inside the cell, then merge with the surface to
remove waste

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Yeast
You may be familiar with fungi from seeing mushrooms and toadstools. Yeast are
single celled fungi. They are used by brewers and wine-makers because they
convert sugar into alcohol, and by bakers because they can produce carbon
dioxide to make bread rise.

Yeast cells have a cell wall, like plant cells, but no chloroplasts.
Yeast can reproduce by producing a bud. The bud grows until it is large enough
to split from the parent cell as a new yeast cell.
Reproduction
Animal reproduction
Gametes
Humans typically reproduce through sexual reproduction. Sexual reproduction
produces offspring that are unique individuals. Half of their genes come from
each parent.

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Sex cells are called gametes. These are sperm and eggs (or ova) in animals, and
pollen and ova in plants
 eggs (or ova ) are female gametes
 sperm are male gametes
Gametes have adaptations to increase the chances of their success.
Sperm cells have many adaptions:
 are produced in large numbers to increase the chance of reaching an egg
cell
 a tail to move them towards an egg cell
 many mitochondria to provide energy
 an acrosome (part of the tip of the head) that releases enzymes to digest
the egg membrane

Egg cells have many adaptions too:

 a large volume of cytoplasm to store food
 a hard outer covering to only allow access to only one sperm cell
 bigger in size when compared to the sperm cell - it would take 15 000
sperm to equal the size of a single egg

Fertilisation
In sexual reproduction, gametes fuse together. The nucleus of a male gamete
and the nucleus of a female gamete join (fuse), and a single new cell is formed.
This is called fertilisation.
There are two types of fertilisation.
 External fertilisation – gametes fuse outside the body e.g., fish, and
amphibians such as frogs, toads, salamanders, and newts.

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  Internal fertilisation – gametes fuse inside the body e.g., mammals, birds,
reptiles.
The male reproductive system

Figure caption,
The parts of the human male reproductive system. The bladder empties into the
urethra but is not part of the reproductive system
The human male reproductive system contains these parts:
 glands
 sperm ducts
 urethra
 penis
 testes
Testes
The two testes (one of them is called a testis) are contained in a bag of skin
called the scrotum. The testes have two functions:
 to produce millions of male gametes (sex cells) called sperm
 to make male sex hormones, which affect the way a man's body develops
The scrotum helps maintain the correct temperature for sperm production. The
two testes produce sperm and, to do this, the temperature of the testes needs to

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be cooler than normal body temperature. This is why the scrotum is located
outside of the body.
Sperm duct and prostate gland
The prostate is a small gland about the size of a ping-pong ball, located behind
the base of the penis. It is important because it supplies part of the fluid which
mixes with sperm as it flows from the testes along the sperm ducts.
The fluids provide the sperm cells with nutrients. The mixture of sperm and fluids
is called semen.
Penis and urethra
The penis has two functions:
 to pass urine out of the man's body
 to pass semen out of the man's body
The urethra is the tube inside the penis that can carry urine or semen. A ring of
muscle makes sure that there is no chance of urine and semen getting mixed up.
Summary

Structure Function

Sperm
duct Thick-walled tube that transports sperm cells from the testes

Prostate
gland Adds fluid to the sperm as it passes along the sperm duct

Testes Produce sperm and make male sex hormones

Tube inside the penis that carries urine or semen out of the man’s
Urethra body

To pass urine and semen out of the man's body. In reproduction it

Penis carries sperm to the vagina

Semen Mixture of sperm and fluids

External sac of skin that encloses the testes. Helps maintain the
Scrotum correct temperature for sperm production

The female reproductive system

The female reproductive systemThe human female reproductive system contains
these parts:

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Figure caption,
The parts of the human female reproductive system. The bladder empties into
the urethra but is not part of the reproductive system
 oviducts
 ovaries
 uterus
 cervix
 vagina
Ovaries
Each ovary is connected to the uterus by an oviduct. This is sometimes called a
Fallopian tube or egg tube. The oviduct is lined with cilia, which are tiny hairs on
cells.
Roughly every month, an egg develops, becomes mature and is released from an
ovary. The cilia waft the egg along inside the oviduct and into the uterus.
One egg is released a month from alternating ovaries
Uterus and cervix
The uterus, also called the womb, is a muscular bag with a soft lining. The uterus
is where a baby develops until it is born.

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The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in
place while the woman is pregnant and protects against infection.
Vagina
The vagina is a muscular tube that leads from the cervix to the outside of the
woman's body.
A man's penis goes into the woman's vagina during sexual intercourse.
Summary

Structu
re Function

Contains hundreds of undeveloped female eggs. Eggs develop, become

mature and are released from an ovary. One egg is released a month
Ovary from alternating ovaries

A tube that links an ovary to the uterus. It transports the egg from the
Oviduct ovary to the uterus. Fertilization occurs here

Uterus Where a baby develops until it is born

Ring of muscle at the lower end of the uterus. Keeps the baby in place
Cervix while the woman is pregnant and protects against infection

Leads from the cervix to the outside of the woman's body. Allows entry
Vagina of the penis during sexual intercourse

The menstrual cycle

The female reproductive system includes a cycle of events called the menstrual
cycle. This starts after a female has reached puberty. Each menstrual cycle lasts
about 28 days, but it can be slightly less or more than this. The cycle stops while
a woman is pregnant. These are the main features of the menstrual cycle:
 The start of the cycle, day 1, is when bleeding from the vagina begins. This
is caused by the loss of the lining of the uterus, with a little blood. This is
called menstruation or having a period.
 By the end of about day 5, the loss of blood stops. The lining of the uterus
begins to re-grow and an egg cell starts to mature in one of the ovaries.
 At about day 14, the mature egg cell is released from the ovary. This is
called ovulation. The egg cell travels through the oviduct towards the
uterus.
 If the egg cell does not meet with a sperm cell in the oviduct, the lining of
the uterus begins to break down and the cycle repeats.

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Fertilisation happens if the egg cell meets and joins with a sperm cell in the
oviduct.
 the fertilised egg then imbeds to the lining of the uterus
 the woman has become pregnant, the lining of the uterus does not break
down
 menstruation does not happen
Human fertilisation
Image gallerySkip image gallery

1.
Image caption,
The human female reproductive system working during reproduction and
fertilisation. The egg is released from the ovary and moves toward the oviduct.

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 2.
Image caption,
The egg cell is released from the ovary into the oviduct. A sperm has been
ejaculated into the vagina and is travelling up the cervix

3.
Image caption,
The egg and sperm meet at the oviduct and the process of fertilisation begins.
1 of 3
Previous imageNext image
Slide 1 of 3, , The human female reproductive system working during
reproduction and fertilisation. The egg is released from the ovary and moves
toward the oviduct.
End of image gallery
Fetal development and birth
Fertilisation happens when an egg cell meets with a sperm cell and joins with it.

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The fertilised egg divides to form a ball of cells called an embryo.
The embryo attaches to the lining of the uterus. It begins to develop into a fetus
and finally into a baby.
Development of the fetus

Figure caption,
A fetus develops in the uterus into a baby ready to be born
The fetus relies upon its mother as it develops. These are some of the things it
needs:
 protection against knocks and bumps, and temperature changes
 oxygen for respiration
 nutrients (food and water)
The developing fetus also needs its waste substances removing.
The fetus is protected by the uterus and the amniotic fluid, a liquid contained in a
bag called the amnion.
The placenta
The placenta is an organ responsible for providing oxygen and nutrients, and
removing waste substances. It grows into the wall of the uterus and is joined to
the fetus by the umbilical cord.
The mother's blood does not mix with the blood of the fetus, but the placenta lets
substances pass between the two blood supplies:
 oxygen and nutrients diffuse across the placenta from the mother to the
fetus

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  carbon dioxide and other waste substances diffuse across the placenta
from the fetus to the mother

Image caption,
The blood of the mother and fetus do not mix, but substances diffuse across the
placenta
Birth

Image caption,
Some babies are born too early and need to put into a warm incubator, where
they may also be helped to breathe
It takes about 40 weeks for a baby to develop in the uterus. This time is called
gestation. After this, the baby is ready to be born. The cervix relaxes and muscles
in the wall of the uterus contract. Waves of muscle contraction push the baby out
of the mother's body through the vagina. A new baby is born!

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Puberty
The reproductive system of a child is not mature. It needs to change as a boy or
girl develops into an adult, so that the system is fully working. The time when the
changes happen is called puberty.

Girls develop breasts and start their periods. Boys develop a deeper voice and
facial hair will start to appear.
The average age for girls to begin puberty is 11, while for boys the average age
is 12.
But it's different for everyone, so don't worry if you reach puberty before or after
your friends and classmates.
It's completely normal for puberty to begin at any point from the ages of 8 to 14
and the process can take up to four years for girls and six years for boys.
The changes happen because of sex hormones produced by the testes in boys
and by the ovaries in girls. Some changes happen in both boys and girls, while
others just happen in boys or girls.
Here are some changes that happen to both boys and girls:
 underarm hair grows
 pubic hair grows
 sweat more
 emotional changes occur
 growth rate increases
 acne can develop
Boys are generally taller than girls, except for the ages 12 and 13 when girls are
taller than boys.
The time between puberty and adulthood is called adolescence.
Boys

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Here are some changes that happen only to boys:

 voice breaks (gets deeper)

 testes and penis get bigger
 testes start to produce sperm cells
 shoulders get wider
 hair grows on face and chest
 may have "wet dreams" (involuntary ejaculations of semen during sleep)
Girls
Here are some changes that happen only to girls:

 breasts develop
 ovaries start to release egg cells (the menstrual cycle starts)
 a white vaginal discharge that keeps the vagina clean and moist, and
protects it from infection, is produced

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  hips get wider
Contraception
Contraception is the deliberate use of artificial methods or techniques to stop
pregnancy. It can be used to plan when people have children and how many
children they have.There are four contraceptive methods used to prevent a
pregnancy:
 mechanical
 chemical
 surgical
 natural

Mechanical

Example Method Advantage Disadvantage

A barrier that Easily obtained. Protects

Male prevents sperm against Sexually Transmitted Unreliable if not
condom entering the vagina. Infections STIs (e.g. HIV). used properly.

A barrier that
Female prevents sperm Easily obtained. Protects Unreliable if not
condom reaching an egg. against STIs (e.g. HIV). used properly.

Chemical

Example Method Advantage Disadvantage

Contraceptiv Taken regularly by the Very reliable Female needs to remember to

e pill female. Stops eggs take the pill. Side effects
being released include weight gain, mood
swings or an increased risk of

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Example Method Advantage Disadvantage

blood clots. Does not protect

against STIs.

A small tube placed

under the skin of the
upper arm. Releases
hormones slowly over a Very reliable.
long period of time. Can work for
Contraceptiv Stops eggs being up to 3 Does not protect against STIs.
e implant released years. Can prevent menstruation.

Surgical

Example Method Advantage Disadvantage

Sperm tubes are cut Virtually Difficult or impossible to

preventing sperm 100% reverse. Does not protect
Vasectomy entering the penis. reliable. against STIs

Oviducts are cut Virtually Difficult or impossible to

Female preventing fertilisation 100% reverse. Does not protect
sterilisation occurring. reliable. against STIs

Natural

Example Method Advantage Disadvantage

Sexual intercourse is
avoided around the No unnatural Very unreliable especially if the
Rhythm time the egg is product is menstrual cycle is irregular.
method released. used Does not protect against STIs

The natural method is chosen by some groups opposed to contraception for

religious or ethical reasons.
The natural method is chosen by some groups opposed to contraception for
religious or ethical reasons.
Plant reproduction

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Flower structure

A flower is the reproductive part of flowering plants. Flowers have colourful

petals. The petals surround the male and female parts of the flower.
The male parts are called stamens,The female parts are called carpels.
Stamens produce fine grains, called pollenCarpels produce ovules.
The table describes the main parts of a flower and their functions:

Structu
re Function

Sepals Protect the unopened flower

Petals May be brightly coloured to attract insects

Stamen The male parts of the flower. Each consists of an anther held up on
s a filament

Anthers Produce pollen grains, the male sex cells

Carpel The female part of the flower (consists of an ovary, a stigma, and

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Structu
re Function

usually a style.)

Stigma The top of the female part of the flower which collects pollen grains.

Style The pollen tubes grow through this

Ovary Produces and contains the female sex cells, the ovules

Contains the female sex cell. Once fertilised an ovule becomes a

Ovule seed

Nectary Produce a sugary solution called nectar, which attracts insects

Pollination
During plant reproduction, pollen grains need to move to the stigma of a flower.
This is called pollination.
Insects can pollinate flowers, and so can the wind. Insect-pollinated flowers are
different in structure from wind-pollinated flowers. This table describes some
differences:
There are two types of pollination:
 self pollination - pollen from an anther of the same flower or same plant
arrives at the stigma of the flower. Examples of self-pollinating plants
include wheat, barley, rice, tomatoes and potatoes.
 cross pollination - the transfer of pollen from an anther of a flower of one
plant to the stigma of the flower of another plant, but of the same species.
Most plants use cross pollination.
Insects can pollinate flowers, and so can the wind. Insect-pollinated flowers are
different in structure from wind-pollinated flowers. This table describes some
differences:

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30
Examples of plants that use insects for cross-pollination include apples, plums,
pears, daffodils, heather, lavender, and most flowering plants.
Examples of plants that use wind for cross pollination include grasses, dandelions
and maple trees.
Many plants that are capable of self-pollinating can also be cross pollinated.
We depend upon pollination by insects, including the honeybee, for many of our
crops.
Seeds and fruit
A pollen grain starts to grow if it lands on the stigma of a flower of the correct
species.
A pollen tube grows through the style of the flower until it reaches an ovule
inside the ovary.
The nucleus of the pollen grain (the male gamete) then passes along the pollen
tube and joins with the nucleus of the ovule (the female gamete).
This process is called fertilisation.

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The slideshow explains what happens:
Image gallerySkip image gallery

1.
Image caption,
A pollen grain is transferred from one flower to another. A pollen tube grows from
the stigma to the ovary.

2.
Image caption,
The nucleus of the pollen grain passes through the pollen tube and joins with the
egg cell inside an ovule in the ovary.

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 3.
Image caption,
The fertilised egg cell develops into an embryo.
1 of 3
Previous imageNext image
Slide 1 of 3, , A pollen grain is transferred from one flower to another. A pollen
tube grows from the stigma to the ovary.
End of image gallery
After fertilisation, the female parts of the flower develop into a fruit:
 the ovules become seeds
 the ovary wall becomes the fleshy part of the fruit that we eat
Seeds
A seed has three main parts:
 embryo – the young root and shoot that will become the adult plant
 food store – starch for the young plant to use until it can carry out
photosynthesis
 seed coat – a tough protective outer covering

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 

Structu
re Function

Testa This is the seed coat. It surrounds the seed and is tough and waterproof

Radicle The young root that will become the adult plant below ground

The young shoot or stem that will become the adult plant above ground.
Plumule The plumule grows after the radicle.

A food store – starch for the young plant to use until it is able to carry
Cotyledo out photosynthesis. Cotyledons are the first leaves to emerge from the
n soil when a seed germinates.

A small opening in the seed coat (Testa) that lets water move into the
Micropyl seed. The seed can then swell and split the seed coat for the young
e plant to emerge

Germination
Germination occurs when a new plant grows out from a seed embryo. All seeds
require three conditions for successful germination:

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  Water
 Oxygen
 Warmth
Investigating germination
Apparatus
Five small tubes with labels and stoppers or lidsCress seedsLabelsCotton
woolDark boxFridgeConical flask and stopperNitrogen gas
Method
1. Label the five tubes A, B, C, D and E
2. Put a small ball of cotton wool into each tube
3. Add a few drops of water to soak the cotton wool
4. Add the damp cotton wool to tubes A, B, C and D
5. Add dry cotton wool to tube E
6. Add 20 cress seeds to each tube
o Place A in the dark box at room temperature: wet, warm, oxygen
and dark
o Place B in the fridge: wet, cold, oxygen and dark

o Place C in light at room temperature: wet, warm, oxygen and light

o Place D in a conical flask flushed with nitrogen gas to remove

oxygen gas and stoppered: wet, warm, light, no oxygen
o Place E in the dark box at room temperature; dry, warm, oxygen and
dark
7. Leave for about three days and record your results in a suitable table.
Conclusion
The three conditions needed for germination to occur are water, oxygen and
warmth

Conditions
(WOW!) Reason

Allows the seed to swell and split. Also lets the chemical reactions
Water involved in the growth of the new plant to take place

Needed for respiration, the process which provides the energy

Oxygen needed to carry out cell division and growth

Warmth Needed for respiration and cell division

A way to remember the three conditions is:

WOW! = Water Oxygen Warmth

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As the new plant grows, it produces roots which take in water and minerals from
the soil and produces leaves on its shoots which carry out photosynthesis to
make food for the plant.

Image caption,
Sycamore maple seed – ideal for wind dispersal
Dispersal
Plants compete with each other for factors such as:
 light
 water
 space
 minerals in the soil
Seed dispersal is the spreading of seeds away and apart from each other and
from the parent plant. It is done to reduce competition between the parent plant
and the new plants, and between the new plants.
The table describes the most common methods of seed dispersal:

Method Detail Examples

Dandelion,
Wind Seeds have lightweight parts, wings or parachutes sycamore

Brightly coloured and tasty fruits contain seeds with Tomato, plum,
Animals indigestible coats, so that the seeds pass through the raspberry,
(inside) animal’s digestive system undamaged grape

Animals Fruits have hooks that attach them to the fur of Goose grass,
(outside) passing animals burdock

Self- Have a pod that bursts open when ripe, throwing the
propelled seeds away from the plant Pea pod

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Investigating dispersal
Seeds dispersed by the wind are easier to investigate than seeds dispersed by
other methods. For example, you could release sycamore seeds and measure the
distance they travel. Factors that could affect the distance travelled by a
sycamore seed include:
 the height from which it is released
 the surface area of the wings
 the mass of the seed
 the wind speed

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