Question
The diagram shows an alveolus from a healthy human lung with type I and II pneumocytes and phagocytes.
What are the main functions of these cells?
▶️Answer/Explanation
Answer: D
Explanation:
1. Type I pneumocyte – Gas exchange
- These are very thin squamous epithelial cells.
- They make up 95% of the alveolar surface area.
- Their thinness allows for rapid diffusion of oxygen and carbon dioxide.
- Main function: Gas exchange
2. Type II pneumocyte – Production of surfactant
- These are cuboidal cells and smaller in number but important.
- They secrete pulmonary surfactant, which:
- Reduces surface tension in the alveoli.
- Prevents alveoli from collapsing during exhalation.
- Main function: Production of surfactant
3. Phagocyte – Ingestion of pathogens
- These are macrophage-type immune cells.
- They:
- Patrol the alveolar surface.
- Engulf (phagocytose) bacteria, dust, and dead cells.
- This keeps the alveoli sterile and clean.
- Main function: Ingestion of pathogens
WHY OTHER OPTIONS ARE WRONG:
Option A and B say phagocytes produce antibodies — that’s false. Only B cells/plasma cells produce antibodies, not phagocytes.
Option C has the Type I and II functions flipped — surfactant comes from Type II, not Type I.
Question
The graph shows the concentration of the lipid lecithin in the amniotic fluid surrounding the fetus during normal gestation. This lipid is produced in the lungs of the fetus and acts as a surfactant.
What problem may occur in a baby born before 34 weeks gestation?
A. Type I pneumocytes do not produce sufficient surfactant for lungs to inflate.
B. There are no type II pneumocytes.
C. The alveolar walls stick together.
D. The alveoli are too large.
Answer/Explanation
Answer: C. The alveolar walls stick together.
Explanation:
- Lecithin is a type of surfactant made by type II pneumocytes in the lungs of a developing baby. Its main job is to reduce surface tension inside the tiny air sacs of the lungs, called alveoli. This helps keep them open so the baby can breathe properly after birth.
- According to the graph, lecithin levels stay very low until around 32–34 weeks of gestation. Before this time, there’s not enough surfactant to prevent the alveoli from collapsing.
- So, if a baby is born before 34 weeks, their lungs may not have enough surfactant. As a result, the alveolar walls can stick together when the baby breathes out, making it very hard to take the next breath in. This condition is called neonatal respiratory distress syndrome (NRDS) and is common in premature babies.
Why the Other Options Are Incorrect:
A. Type I pneumocytes are responsible for gas exchange, not surfactant production.
B. Type II pneumocytes are present even in early development, but they aren’t fully active yet.
D. The size of alveoli isn’t the problem here — the real issue is their collapse from lack of surfactant.
Final Takeaway:
A baby born before 34 weeks may not have enough surfactant, which causes alveoli to collapse by sticking together. This is why option C is correct.
Question
Pressure changes inside the thorax cause the movement of air in and out of the lung alveoli during ventilation. Alveolar pressure correlates to thoracic pressure. The diagram shows pressure
changes in lung alveoli during ventilation in relation to normal atmospheric pressure. What causes forced movement of air out of the lungs at T?
Answer/Explanation
Answer: B
Explanation:
Forced exhalation (like when blowing out candles or during heavy breathing) needs extra muscle help.
- Internal intercostal muscles: Pull the ribcage down and in, making the chest cavity smaller.
- Abdominal muscles: Contract to push the diaphragm upward, squeezing the lungs even more.
This increases pressure in the lungs above atmospheric pressure, causing air to be forcefully pushed out — exactly what we see at point T on the graph.
Why Other Options Are Wrong:
A. External intercostals contract + diaphragm relaxes → Mixed-up info. External intercostals are for inhalation, not exhalation.
C. Internal intercostals contract + diaphragm contracts → Diaphragm contraction = inhalation, not exhalation. Contradiction!
D. External intercostals relax + abdominal muscles relax → Relaxing muscles doesn’t cause forced movement. This is more like normal passive exhalation, not what’s shown in the graph (which is forced).
Final Takeaway:
At T, alveolar pressure is above atmospheric pressure, meaning air is being forcefully exhaled. This happens when internal intercostal and abdominal muscles contract, squeezing the lungs.
That’s why B is the correct choice.
Question
Where in the body are type I pneumocytes found?
Alveoli
Nephrons
Capillaries
Trachea
Answer/Explanation
Answer: A. Alveoli
Explanation:
Type I pneumocytes are thin, flat cells that line the alveoli in the
lungs. Their main job is to form the surface through which oxygen and carbon dioxide can pass during gas exchange. Because they are so thin, gases can move quickly between the air in the alveoli and the blood in nearby capillaries.
Options Evalution:
A. Correct – Type I pneumocytes are found in the alveoli, where they form the thin walls needed for gas exchange.
B. Incorrect – Nephrons are found in the kidneys and help filter blood to make urine; they do not contain pneumocytes.
C. Incorrect – Capillaries are small blood vessels near the alveoli but do not contain type I pneumocytes themselves.
D. Incorrect – The trachea is a windpipe that carries air to the lungs and is lined with different types of cells, not pneumocytes.
Question
Which is an adaptation to increase rates of gas exchange in the lung?
Small surface area
Dry surface
High vascularization
Muscular alveoli
Answer/Explanation
Answer: C. High vascularization
Explanation:
Gas exchange in the lungs happens in the alveoli. To be efficient, the lungs need features that increase diffusion, such as a large surface area, moist surface, thin walls, and a good blood supply (high vascularization).
Option Evaluation:
A. Incorrect – Small surface area
Reduces space for diffusion. Lungs need a large surface area for efficient gas exchange.
B. Incorrect – Dry surface
Gases must dissolve in moisture to diffuse. A dry surface would slow gas exchange.
C. Correct – High vascularization
A dense network of capillaries keeps oxygen and carbon dioxide moving, maintaining concentration gradients for fast diffusion.
D. Incorrect – Muscular alveoli
Alveoli are elastic, not muscular. Muscles help in breathing, not in the structure of alveoli.
Question
For what reason do large organisms need specialized gas exchange structures?
A. They have a large surface area to volume ratio.
B. There is a short distance to the centre of their body
C. They have a relatively small surface in contact with the outside
D. Their skin is impermeable to respiratory gases.
▶️Answer/Explanation
Answer: C. They have a relatively small surface in contact with the outside
Explanation:
Large organisms need specialized gas exchange structures because simple diffusion through the body surface is not enough. This is due to their relatively small surface area compared to their large volume, and the long-distance gases would have to travel inside the body.
Options Evaluation:
A. Incorrect – Large organisms have a small surface area to volume ratio, meaning their surface is not large enough compared to their volume for efficient gas exchange by diffusion alone.
B. Incorrect – The distance from the surface to the center of large organisms is long, which slows diffusion, not short.
C. Correct – Large organisms have a relatively small surface area in contact with the outside environment compared to their volume, so they require specialized organs (like lungs or gills) to increase surface area and speed up gas exchange.
D. Incorrect – While some animals have impermeable skin, the main reason large organisms need special gas exchange structures is due to their surface area-to-volume ratio, not because their skin is impermeable.
Question
What can be seen in a plan diagram of a leaf?
A. Spongy cells and surface of the upper epidermis
B. Chloroplasts in palisade cells and position of waxy cuticle
C. Vascular bundles and thickness of palisade mesophyll
D. Guard cells and distribution of air spaces
▶️Answer/Explanation
Answer: C. Vascular bundles and thickness of palisade mesophyll
Explanation:
A plan diagram shows the leaf from above (top view). In this view, vascular bundles (veins) appear as spots, and the thickness of the palisade mesophyll can be represented by the number of cell layers across the surface. Internal details like chloroplasts, waxy cuticle, guard cells, and air spaces are better seen in cross-section, not plan.
Options Evaluation:
A. Incorrect – Spongy cells are internal and not visible in plan view.
B. Incorrect – Chloroplasts and waxy cuticle are internal features seen in cross-section.
C. Correct – Vascular bundles and palisade mesophyll thickness can be shown in plan view.
D. Incorrect – Guard cells and air spaces are not visible in plan view.
Question
What occurs at gas exchange surfaces in the lungs of mammals?
I. Gases diffuse across a moist surface.
II. Concentration gradients are maintained by ventilation.
III. Water is lost.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Answer: D. I, II and III
Explanation:
In mammal lungs, gas exchange happens in tiny air sacs called alveoli. Oxygen moves from the air inside the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli to be breathed out. For this to work well, three important things happen:
- The surface where gases exchange is moist. This moisture helps gases dissolve and pass through easily.
- Breathing (ventilation) keeps fresh oxygen coming in and carbon dioxide going out, which keeps a difference in gas levels (called a concentration gradient). This difference makes gases move in the right direction.
- Because the surface is moist and open to the air, some water evaporates and is lost.
Answer Evaluation:
A. Incorrect – Statements I and II are true. The moist surface helps gases pass through, and breathing keeps the gas levels balanced. But it leaves out the fact that water is lost, which also happens.
B. Incorrect – It says gases pass through a moist surface and water is lost, but it ignores the important role of breathing (ventilation) in keeping the gas levels right.
C. Incorrect – It mentions ventilation and water loss,but misses that gases need a moist surface to diffuse properly. Without moisture, gas exchange can’t happen well.
D. Correct – All three statements are true and important. Gases diffuse across a moist surface, breathing keeps gas levels balanced, and water is lost through evaporation.
Question
What is always a consequence of the evaporation of water from mesophyll cells in leaves of a healthy plant?
A. Plasmolysis occurs in mesophyll cells.
B. Photosynthesis stops.
C. Stomata close to reduce transpiration.
D. Water moves up the stem in the xylem.
▶️Answer/Explanation
Answer: D. Water moves up the stem in the xylem.
Explanation:
When water evaporates from the mesophyll cells inside a leaf, it creates a kind of “pull” that draws more water up from the roots through tiny tubes called xylem. This movement is part of what we call the transpiration stream. It helps carry water and nutrients from the soil all the way up to the leaves.
Let’s look at the other options:
A is wrong because plasmolysis happens only when a plant loses too much water and gets stressed, not during normal water evaporation.
B is wrong because photosynthesis keeps going; in fact, moving water helps photosynthesis by keeping cells healthy.
C is wrong because stomata usually stay open during normal conditions to let in carbon dioxide for photosynthesis, even though some water evaporates.
So, the key thing that always happens when water evaporates inside a healthy leaf is that water moves upward through the plant’s xylem vessels.
Question
A plant is allowed to photosynthesize in an atmosphere containing radioactive 14C. Where in the plant stem would radioactive sugars be found?
▶️Answer/Explanation
Answer: B
Explanation:
Image Analysis of Plant Stem (TS – Transverse Section)
Let’s decode each label:
- A – Epidermis (outermost protective layer)
- B – Phloem (pink, dense area near the outside of vascular bundle)
- C – Xylem (larger, open vessels more towards the centre)
- D – Cortex/Parenchyma (filler ground tissue)
Radioactive 14C and Photosynthesis
- When a plant photosynthesises in radioactive ¹⁴CO₂, the carbon gets fixed into glucose (sugar).
- These sugars are then transported through the plant via the phloem — the sugar highway!
So…
Where would radioactive sugars go?
Into the phloem, because that’s where the transport of organic products (like glucose/sucrose) happens.
Question
The apparatus in the diagram was used to assess the effects of factors on transpiration rates.
Which factor would be a controlled variable in an experiment designed to assess the effects of temperature on transpiration rate?
A. The opening and closing of stomata
B. The intensity of light striking the plant
C. The height of the water in the reservoir
D. The evaporation of water from the leaves
▶️Answer/Explanation
Answer: B. The intensity of light striking the plant
Explanation:
When studying how temperature affects transpiration rate, all other factors that can influence transpiration need to be kept the same. These factors that stay constant to make the experiment fair are called controlled variables. Controlling variables ensures that any change in transpiration is only due to temperature, not something else.
Options Evaluation:
A. Incorrect – The opening and closing of stomata is not something you can directly control; it is affected by environmental factors like light and humidity. It’s more a response, not a controlled variable.
B. Correct – Light intensity directly affects transpiration because it influences stomatal opening. To study temperature’s effect alone, light intensity must be kept constant.
C. Incorrect – The height of water in the reservoir changes as transpiration happens and is measured as part of the experiment, so it cannot be controlled.
D. Incorrect – Evaporation of water from leaves is what you are measuring (or related to transpiration), so it is the outcome, not a controlled variable.