1.
On a bright sunny day water weeds growing in an aquarium were actively giving off bubbles
of.gas. Use this information to answer questions that follow :
(a) Of what gas do these bubbles consist. Name the process occurring in the water weed
thatresulted in evolution of these bubbles. ½+ ½
(b) Briefly describe the reactions occurring in the leaves of the water weeds leading to
the evolution of these bubbles. 1
The process that takes place first in the photolysis of water is H+ and OH- ions with the help
of energy from sunlight. The hydroxyl ions combine to form hydrogen peroxide 2OH —>
H2O2 which decompose to give molecular oxygen i.e. 2H2O2 ——> 2H2O + O2.
(c). Will the rate of release of the bubbles be affected when the aquarium is exposed
to green light? Justify your answer. 1
The rate of release of bubbles will stop when the aquarium is exposed to green light because
the only light which plant reflects is green light and in this way the plant will not get light
and eventually photosynthesis will stop.
2. (a) How can pancreas help in digestion and also regulate blood sugar?
The pancreas secretes digestive enzymes such as pancreatic amylase (for starch digestion),
pancreatic lipase (for fat digestion), and proteases (for protein digestion). These enzymes are
released into the small intestine where they break down food into simpler molecules that can be
absorbed.
2 (b). A person was detected with stones in gallbladder. The doctor advised the removal of the
organ. How will it affect the digestive system of the person? 1
The gallbladder stores and concentrates bile produced by the liver, which aids in the digestion
and absorption of fats in the small intestine. After gallbladder removal, bile flows directly from
the liver into the small intestine. Digestion of fats may become less efficient, leading to
symptoms like diarrhoea or fat malabsorption, especially after consuming fatty meals.
3. (a) Breathing and respiration are not synonymous. Why? 1
Breathing refers to the physical process of inhaling oxygen and exhaling carbon dioxide. It
involves the movement of air into and out of the lungs.
Respiration is a biochemical process where cells use oxygen to release energy from glucose. It
occurs within cells and involves complex metabolic reactions such as glycolysis, Krebs cycle,
and oxidative phosphorylation.
b (i) Under normal conditions, what is the rate of breathing per minute? 1
Under normal conditions, the rate of breathing per minute in humans is approximately 12-18
breaths.
(ii) Why does the rate of breathing increase by 20 to 25 times during vigorous exercise? 1
During vigorous exercise, muscles require more oxygen to produce energy through aerobic
respiration. The rate of breathing increases by 20 to 25 times to meet this increased demand for
oxygen and to remove the excess carbon dioxide produced as a by-product of increased
metabolism.
4. a) Explain the relationship between the respiratory system and the circulatory system. 1
Relationship Between Respiratory System and Circulatory System:
•The respiratory system supplies oxygen to the blood and removes carbon dioxide from it.
•The circulatory system transports oxygenated blood from the lungs to the tissues and returns
deoxygenated blood to the lungs.
•Together, they ensure that oxygen is delivered to cells for cellular respiration, and carbon
dioxide is removed from the body.
b) How does the respiratory system provide oxygen to the body's cells and remove carbon
dioxide?2
The respiratory system provides oxygen to the body’s cells and removes carbon dioxide through
the process of breathing and gas exchange in the lungs. Oxygen from the air is taken in during
inhalation and enters the bloodstream through tiny blood vessels surrounding the alveoli in the
lungs. Carbon dioxide, produced as a waste product in cells, is removed from the bloodstream
and expelled from the body during exhalation. This continuous exchange ensures cells receive
oxygen for cellular respiration and expel carbon dioxide, maintaining the body’s metabolic
balance.
5. Justify the following statements : (3x1=3)
a) Trachea lined by ciliated epithelium.
The ciliated epithelium in the trachea helps in trapping dust particles and other foreign
substances, preventing them from entering the lungs.
b) Lungs contain residual volume of air .
Residual volume refers to the air left in the lungs after maximal expiration, which ensures that
the lungs stay partially inflated and gas exchange can continue even between breaths.
c) RBCs in our blood increase when we go to high altitudes
At high altitudes, where oxygen concentration is lower, the body compensates by producing
more red blood cells (RBCs) to carry more oxygen to tissues. This adaptation helps in
maintaining adequate oxygen supply to cells.
CASE BASED QUESTIONS
CASE 1
A group of students decided to investigate the effects of physical exercise on respiration. They
designed an experiment where they measured their breathing rates before and after different
levels of physical activity. The students used a simple method of counting breaths per minute and
recorded their observations.
(a) After participating in light physical activity, the students noticed a slight increase in their
breathing rates. Explain why this increase in breathing rate occurred and what
physiological process is responsible for it.
(b) During intense physical exercise, the students experienced a significant increase in their
breathing rates compared to rest. Describe the role of oxygen in the body during
strenuous exercise and why increased respiration is necessary.
(c) One of the students, Sarah, observed that after a period of vigorous exercise, her
breathing rate remained elevated even during rest for a short while. Provide a scientific
explanation for this phenomenon.
OR,
⒞ While analyzing their data, the students found that a classmate who has been practicing
deep breathing techniques showed less increase in breathing rate after exercise compared
to others. Explain how deep breathing exercises can impact respiration and why this
classmate had a different response.
1+1+2 = 4
A) The increase in breathing rate after light physical activity occurs
because the body needs more oxygen to supply to the muscles and
tissues that are working. During exercise, muscles produce more
carbon dioxide and lactic acid due to increased metabolic activity. This
buildup of carbon dioxide and lactic acid triggers chemoreceptors in
the blood vessels and brain to send signals to the respiratory center in
the brain. As a result, the rate and depth of breathing increase,
allowing more oxygen to enter the body and carbon dioxide to be
removed.
B) During intense physical exercise, muscles require more energy to
contract rapidly and forcefully. This energy is primarily produced
through anaerobic respiration (in the absence of oxygen) at the start of
exercise, but as the exercise continues, aerobic respiration (with
oxygen) becomes the dominant process. Oxygen is crucial during
strenuous exercise because it is needed for aerobic respiration, which
produces much more ATP (energy currency of cells) compared to
anaerobic respiration. The increased respiration rate ensures that more
oxygen is brought into the body to meet the heightened demand from
the working muscles. This increased oxygen uptake helps to break
down glucose and fatty acids more efficiently, providing sustained
energy for muscle contraction.
C) Sarah’s elevated breathing rate after vigorous exercise during rest
occurs because her body is repaying the oxygen debt accumulated
during exercise. This process helps restore normal levels of oxygen and
carbon dioxide in her body after the increased metabolic demands of
exercise.
Or part) Deep breathing exercises improve lung capacity and efficiency,
allowing for better oxygen exchange and strengthening respiratory
muscles. This classmate likely had a lower increase in breathing rate after
exercise because their lungs were more efficient at oxygen uptake and
they had stronger respiratory muscles, reducing the need for rapid
breathing during physical activity.
CASE 2
The green plants make their food through photosynthesis and are therefore called autotrophs. All
other organisms depend upon green plants for food and are referred to as heterotrophs. Green
plants carry out photosynthesis by using light energy from the sun. The first phase of reactions
are directly light driven therefore called light reactions. The second phase of reactions are not
directly light driven but are dependent on the products of light reactions and are called dark
reactions.The diagram given below is an experiment conducted to study a factor necessary for
photosynthesis.
a)Write the aim of the activity and mention the test performed on the leaf.
The aim of the activity is to test the factors of necessary for photosynthesis. The test performed
on the leaf is the iodine test to detect the presence of starch, which indicates successful
photosynthesis in the leaf.
b) A plant is provided with ideal conditions for photosynthesis and supplied with isotope 14CO2.
Of the two products of photosynthesis glucose and oxygen, which one would be labelled and
why?
Glucose would be labelled with carbon-14 because it incorporates carbon atoms from the
supplied 14CO2 during photosynthesis.
c ) Write two differences between the light and dark phase of photosynthesis.
Light Phase (Light Reactions):
•Occurs in the thylakoid membranes of chloroplasts.
•Converts light energy into chemical energy (ATP and NADPH) used in the dark phase.
Dark Phase (Dark Reactions or Calvin Cycle):
•Occurs in the stroma of chloroplasts.
• Uses ATP and NADPH from the light reactions to convert carbon dioxide (CO2) into glucose
and other organic molecules.
OR,
⒞ Given below is the cross section of a leaf
(i) Identify ‘A’ and choose the correct combination of plots provided in the following table.
A Description Function
1.
Chlorophyll A green coloured pigment Essential for photosynthesis
2.
Chloroplast A cell organelle Conducts photosynthesis
3.
Stomata Opening Gaseous exchange
4.
Chloroplast A green coloured pigment Essential for photosynthesis
(ii) What is the role of ‘B’? 1+1+2
=4
B is guard cells which helps to regulate the opening and closing of stomata to control gas
exchange (including CO2 uptake and O2 release) and minimize water loss through transpiration
in plants.
CASE 3
During a science laboratory activity, some sugar solution is taken in a test tube and a little
amount of substance is taken in powdered form named ‘P’. The test tube is allowed to stay still
for some time while the top is covered with a cork. On removing the cork it gives out a
characteristic smell ‘Y’. A gas ‘Z’ evolution takes
place that is allowed to pass through lime water.
a) Identify the powder ‘P’, the smell ‘Y’.
Powder P is yeast and smell Y is ethanol.
b)Identify the gas ‘Z’. What happens to the lime water?
Gas Z is carbon dioxide. When CO₂ is passed through lime water (a solution of calcium
hydroxide), it turns milky due to the formation of calcium carbonate (CaCO₃).
c)What type of respiration is observed in the above activity? Explain.
The respiration observed is anaerobic respiration (fermentation). Yeast ferments the sugar
solution in the absence of oxygen, producing ethanol, carbon dioxide, and energy.
OR,
⒞ The pathway of respiration common in all living organisms is A; it occurs in the B and
the products formed are two molecules of C. In presence of oxygen, it completely breaks
down into CO2, H2O and D. Identify A, B, C and D.
1+1+2 = 4
A: Glycolysis
B: Cytoplasm
C: Pyruvate (or pyruvic acid)
D: ATP (Adenosine Triphosphate)
CASE 4
Digestion is a catabolic process in which complex and large components of food are broken
down into their respective simpler forms with the help of various hydrolytic enzymes. The small
intestine is the site of complete digestion of carbohydrates, proteins and fats. It receives the
secretions of the liver, pancreas for this purpose. The food coming from the stomach has to be
made alkaline for the pancreatic enzymes to act on. Fats are present in the intestine in the form of
large globules which makes it difficult for enzymes to act on them. Bile salts break them down
into smaller globules increasing the efficiency of enzyme action.
(a) A and B in the given graph are action spectra of two enzymes. Study the graph and
suggest the names of the two enzymes.
b) What makes the food alkaline?
c) Butter cannot be digested in the stomach. Justify with reason.
OR,
c) Match column I with column II and column III.
Column I Column II Column III
Substrate Enzyme Product
1.
Lactose Lipase Maltose
2.
Fatty acid Amylase Dipeptide
3.
Starch Trypsin Galactose
4.
Protein Lactase Glycerol
1+1+2 = 4
CASE 5
All living cells require energy for various activities. This energy is available by the breakdown of
simple carbohydrates either using oxygen or without using oxygen. The graph below represents
the blood lactic acid concentration of an athlete during a race of 400m and shows a peak at point
D.
a)Mention the site of production of lactic acid in the body cells.
b)What is the cause of lactic acid production in the body of the athlete?
c)Study the graph below that represents the amount of energy supplied with respect to the time
while an athlete is running at full speed. Of the two plots A and B, which one represents aerobic?
Justify your answer.
OR,
⒞ The given graph illustrates the change in lung volume during the process of breathing.
What happens to the diaphragm and ribs during the change from I – II? Explain the state of the
lungs between III – IV?
1+1+2 = 4
