Question 1

A student investigated the rate of oxygen uptake during aerobic respiration in woodlice. Woodlice are arthropods.State the word equation for aerobic respiration. .............................................................................................................................................

Accepted Answer

Respiration using oxygen to break down food molecules is called aerobic respiration. Glucose is the molecule normally used for respiration – it is the main respiratory substrate. Glucose is oxidised to release its energy.The word equation for aerobic respiration is:glucose + oxygen → carbon dioxide + water (+ energy released)

Question 2

All commercial breeds of sheep belong to the species Ovis aries .Define the term species .............................................................................................................................................. The Merino is a breed of sheep that is farmed mainly for its wool. The wool is very thick and is made of lots of very thin hairs. Figure below shows a female Merino sheep with her newborn lamb.

Accepted Answer

A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring. Species are characterized by the fact that they are reproductively isolated from other groups, which means that the organisms in one species are incapable of reproducing with organisms in another species.

Question 3

The presence of hair is a feature that is only found in mammals. State two other features that distinguish mammals from all other vertebrates.1 ................................................................................................................................................2 ................................................................................................................................................

Accepted Answer

Mammals are amazingly diverse animals. They live in nearly every available habitat on Earth—including deep seas, tropical rainforests, and deserts—and they range in size from one-ounce shrews to 200-ton whales. Features that distinguish mammals from all other vertebrates-1) Mammary glands- Unlike other vertebrates, mammals nurse their young with milk produced by mammary glands, which are modified and enlarged sweat glands consisting of ducts and glandular tissues that secrete milk through nipples. 2) Three Bones in the Middle Ear- The three inner ear bones, the incus, the malleus, and the stapes—commonly referred to as the hammer, the anvil and the stirrup—are unique to mammals. These tiny bones transmit sound vibrations from the tympanic membrane (the eardrum) to the inner ear and transform the vibrations into neural impulses that are then processed by the brain.

Question 4

The rate of photosynthesis of terrestrial plants can be determined by measuring the uptake of carbon dioxide.Explain why plants take up carbon dioxide during photosynthesis....................................................................................................................................................

Accepted Answer

Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates. The concentration of carbon dioxide is higher outside the leaf than inside, so, carbon dioxide diffuses in to the leaf. In the process of photosynthesis, carbon dioxide from the atmosphere is incorporated into the leaves through the stomata and is used to synthesis carbohydrates such as glucose and starch which are then utilized for cellular respiration.

Question 5

The rate of photosynthesis of parts of individual leaves can be measured using a hand-held device as shown in the figure.This apparatus allows air to flow through the transparent chamber that encloses part of the leaf. The apparatus measures the carbon dioxide concentration of the air entering and leaving the chamber. Explain how the results from the apparatus can be used to calculate the rate of photosynthesis....................................................................................................................................................

Accepted Answer

The apparatus measures the carbon dioxide concentration of the air entering and leaving the chamber. The rate of photosynthesis is a gross measure of the rate at which a plant captures radiant energy and fixes it in organic carbon compounds.In order to calculate the rate of photosynthesis - the concentration of carbon dioxide at the end should be subtracted from the concentration at the start ; this will give us the change in concentration of carbon dioxide. The value should now be divided with by the time (taken) / per unit time. This will give us the rate of photosynthesis.

Question 6

The rate of photosynthesis of parts of individual leaves can be measured using a hand-held device as shown in the Fig. 1. A student used the apparatus shown in Fig.1 to investigate the effect of temperature on the rate of photosynthesis of the leaves of Chinese plantain, Plantago asiatica , at two different concentrations of carbon dioxide, A and B. Fig. 2 shows the results of the investigation. (i) State one environmental factor that should have been kept constant in this investigation. ..................................................................................................................................... (ii) Describe the effect of temperature on the rate of photosynthesis when carbon dioxide concentration A was supplied. Use the data from Fig. 2 in your answer...................................................................................................................................... (iii) Calculate the percentage increase in the rate of photosynthesis at 30°C when the carbon dioxide concentration was increased from A to B as shown in Fig. 2. Show your working and give your answer to the nearest whole number............................................................. %  (iv) Explain the effect of increasing temperature on the rate of photosynthesis for carbon dioxide concentration B. Use the term limiting factor in your answer...................................................................................................................................... (v) The student concluded that carbon dioxide concentration is the factor limiting the rate of photosynthesis between 30°C and 35°C for the results shown for A in Fig. 2. State the evidence for this conclusion......................................................................................................................................

Accepted Answer

(i) Humidity(ii) It is observed that, when carbon dioxide concentration A was supplied, temperature increases between 10 °C to 30 °C, and rate of photosynthesis also increases. At  approx. 30 °C, the temperature remains constant, when reaches a plateau and there is no change in rate of photosynthesis when temperature reaches a plateau. (iii) The rate of photosynthesis at 30°C when the carbon dioxide concentration was increased from A = 22 μmol per m2 per sThe rate of photosynthesis at 30°C when the carbon dioxide concentration was increased  B = 34 μmol per m2 per sThe percentage increase in the rate of photosynthesis at 30°C when the carbon dioxide concentration was increased from A to B = 34-22 = 12                                                                                                                                                                                                           = 12/34 = 0.3529                                                                                                                                                                                                           = 0.3529 × 100                                                                                                                                                                                                           = 35.29 % ( approx. 36 %)(iv) As the temperature increases, the rate of photosynthesis for carbon dioxide concentration B also increases. As we know that the temperature is the limiting factor for the process of photosynthesis. Increase in temperature increases the kinetic energy of molecules involved in the process of photosynthesis and also increases the  rate of diffusion of carbon dioxide into the leaf. Increase in temperature results in the more effective collisions between substrate molecules and enzymes involved in the process of photosynthesis and more enzyme-substrate complexes are formed.(v) It is observed that the rate of photosynthesis is, higher and continues to increase, if carbon dioxide is increased at all temperatures. A shows that the rate of photosynthesis becomes constant between 30°C and 35°C. So, we can conclude that carbon dioxide concentration is the factor limiting the rate of photosynthesis between 30°C and 35°C for the results shown for A in Fig. 2.

Question 7

An investigation was carried out on Arizona honeysweet, Tidestromia oblongifolia , that grows in Death Valley in California where the highest temperatures may be greater than 45°C. The results are shown in the figure.Predict and explain what would happen to the rate of photosynthesis if the investigation is continued at temperatures higher than 45°C. .............................................................................................................................................

Accepted Answer

Following prediction can be made from the results shown in graph-The rate of photosynthesis remains constant and/or decreases if the investigation is continued at temperatures higher than 45°C. This is because photosynthesis is an enzyme mediated process, at higher temperature the enzymes gets denatured hampering the rate of photosynthesis.

Question 8

Transmission of impulses relies on the flow of ions through the cell membranes of neurones down their concentration gradients. Active transport is responsible for maintaining the concentration gradients of ions across the membranes of neurones.Explain how ions are moved across membranes by active transport....................................................................................................................................................

Accepted Answer

Active transport is an energy-driven process where membrane proteins transport molecules across cells. In active transport this movement s achieved by acting against the formation of an equilibrium, typically by concentrating molecules depending on the various needs of the cell, e.g., ions, sugars, and amino acids. Active transport requires the use of energy (namely ATP) since it takes molecules from a lower to a higher concentration, i.e., against its concentration or electrochemical gradient. Conduction of nerve impulse occurs due to the presence of active and electronic potentials along the conductors. In particular, the sodium-potassium pump is required to maintain cell potentials and can be seen in neuronal action potentials.

Question 9

The area labelled M is a mitochondrion. Explain why mitochondria have an important role in dividing cells.................................................................................................................................................................................................................................................................................................

Accepted Answer

Mitochondria undergo fragmentation during mitosis and are well distributed throughout the cell soma due to their interactions with the ER and cytoskeleton. As a result, cytokinesis can result in the partitioning of roughly equal amounts of mitochondria to daughter cells. They are responsible for aerobic respiration, producing energy for the cell, which they achieve through oxidative phosphorylation. Energy produced during aerobic respiration helps in the movement of chromosomes, making cell wall, making new molecules such as protein/DNA etc.

Question 10

Soybean plants, Glycine max, were grown in two separate plots.Each plot used a carbon dioxide enrichment system to control the atmospheric carbon dioxide concentration.The atmospheric carbon dioxide concentrations in the two plots were kept at: • 370ppm, which is similar to the current atmospheric carbon dioxide concentration • 550ppm, which is a possible future atmospheric carbon dioxide concentration.When the soybean plants were fully grown, scientists calculated the average rates of photosynthesis at regular intervals from 04:00 to 22:00 for both plots.The results are shown in figure given below.Describe and explain the effect of carbon dioxide concentration on the average rates of photosynthesis of the soybean plants from 04:00 to 22:00. Use the data from the figure in your answer....................................................................................................................................................

Accepted Answer

From the given graph the following interpretations are made-1) Photosynthesis starts at, 6:00 am and stops at 8:00 pm. 2) The rate (of photosynthesis) peaks at 12:00 noon. 3) The rate (of photosynthesis) at 550 ppm is greater than at 370 ppm. 4) Both plots follow same trend.Three factors can limit the rate of photosynthesis: light intensity, carbon dioxide concentration and temperature.  At lower carbon dioxide concentrations, carbon dioxide is the limiting factor because an increase in carbon dioxide causes an increase in photosynthesis (rate of photosynthesis is higher in 550pm plot). The rate of photosynthesis increases linearly with increasing CO2​ concentration (from 6:00 am to 12:00 noon). The rate falls gradually, and at a certain CO2​ concentration rise in CO2​ levels has no effect as the other factors such as light intensity become limiting.Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide. Maximum light intensity is at 12:00 noon, therefore the rate of photosynthesis increases gradually upto 12 noon and then gradually starts decreasing due to decreased light intensity as the evening approaches.Also higher temperature causes increased rate of photosynthesis, that is why during the day time (6:00 am to 1:00 pm) the rate of photosynthesis increases linearly and from 2:00 pm to 8:00 pm, the rate of photosynthesis decrease with decrease in temperature.

Question 11

The scientists also made observations of the leaf structure of the soybean plants.Epidermis and mesophyll tissues are adapted for photosynthesis.Complete the table given below by stating two structural features of each of these tissues and explain how each feature is an adaptation for photosynthesis.

Accepted Answer

Epidermis:Mesophyll:

Question 12

When the scientists were working in the plot with a carbon dioxide concentration of 550ppm, their breathing rates were higher than when they worked in the other plot.Suggest why their breathing rates were higher..............................................................................................................................................

Accepted Answer

When the scientists were working in the plot with a carbon dioxide concentration of 550ppm, their breathing rates were higher than when they worked in the other plot because at higher CO2​ concentration, the blood concentration of carbon dioxide increases, the breathing rate increases. This is because the respiratory centre in the medulla oblongata is informed of increasing blood acidity (from blood chemoreceptors) and stimulates faster contraction of muscles controlling ventilation. When the concentration of carbon dioxide in the human body increases, the lungs are signaled to increase their activity and exhale more carbon dioxide.

Question 13

Lugworms live in sand on coastal beaches and are eaten by wading birds. Lugworms feed on diatoms. Diatoms are photosynthetic protoctists that require ammonium ions as a source of nitrogen. Beach sand contains ammonium ions.(i) Construct a food chain for these marine organisms. (ii) There is some evidence that microplastics affect ammonium ions. Affected ammonium ions cannot be used by diatoms. A group of researchers thought that this could affect lugworms living in sand polluted by microplastics. The researchers collected 30 healthy lugworms, all with the same initial mass. They divided them into three groups, A, B and C. Each group contained 10 lugworms. Each group of lugworms was placed in a bucket containing the same mass of beach sand and ammonium ions and: A. biodegradable microplastics B. non-biodegradable microplastics C. no microplastics. The measurements that were recorded at the end of the investigation are shown in the table given below.Describe and explain why the researchers concluded that non-biodegradable microplastics are the most harmful to lugworms. Use the information given in the table  in your answer......................................................................................................................................

Accepted Answer

(i) diatom → lugworm → (wading) bird Diatoms are photosynthetic protoctists that require ammonium ions as a source of nitrogen. Lugworms feed on diatoms to get energy and food. Birds feed on lugworms to get food and energy.(ii) The researchers concluded that non-biodegradable microplastics are the most harmful to lugworms. From the given data, it is observed that, in the bucket of group B, highest number of ammonium ions was present but less ammonium ions are absorbed by the diatoms. Respiration rate of lugworms is also higher in group B. Body mass and volume of lugworm faeces is also the least in group B. Because of higher rate of respiration, lugworms requires to release more energy to find food. Therefore, by the given data, we can say that, non-biodegradable microplastics have negatively affected the digestion of the lugworms. This further results in the slower growth rate of lugworms.

Question 14

Figure below shows some of the many different varieties of potato, Solanum tuberosum, that are cultivated across the world for food. All varieties of S. tuberosum  are classified as the same species. Define the term species ............................................................................................................................................. .

Accepted Answer

A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring. Species are characterized by the fact that they are reproductively isolated from other groups, which means that the organisms in one species are incapable of reproducing with organisms in another species.

Question 15

Potato tubers store starch.Explain why plants store starch....................................................................................................................................................

Accepted Answer

Starch is an insoluble, non-structural carbohydrate composed of α-glucose polymers. It is synthesized by plants to store energy in a dense, osmotically inert form i.e., the carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant.

Question 16

Bacteria are classified in the Prokaryote kingdom.State two features of animal cells that are not found in bacteria.1 ................................................................................................................................................ 2 ................................................................................................................................................

Accepted Answer

Two features of animal cells that are not found in bacteria- 1) Animal cell has nuclear membrane whereas in bacteria genetic material lies in the cytoplasm.2) Animal cell has membrane bound organelles such as mitochondria or chloroplasts which are absent in bacteria.

Question 17

State the word equation for photosynthesis..............................................................................................................................................

Accepted Answer

The word equation for photosynthesis-carbon dioxide + water + sunlight → glucose + oxygen

Question 18

Scientists investigated the effect of light intensity on the rate of photosynthesis in the leaves of eucalyptus trees at two different concentrations of carbon dioxide, A and B. The results are shown in figure below.(i) Suggest and explain why the scientists kept the temperature of the leaves at 20°C while they recorded results. ........................................................................................................................................... (ii) Calculate the percentage increase in the rate of photosynthesis at a light intensity of 1250 arbitrary units when the carbon dioxide concentration was increased from 140ppm to 1000ppm. Show your working and give your answer to the nearest whole number. ............................................................ %(iii) Describe the effect of increasing light intensity on the rate of photosynthesis when the concentration of carbon dioxide was 140 ppm............................................................................................................................................(iv) Explain the effect of increasing light intensity on the rate of photosynthesis when the concentration of carbon dioxide was 1000 ppm. Use the term limiting factor in your answer. ...........................................................................................................................................

Accepted Answer

(i) Enzymes are protein molecules used by living organisms to carry out biochemical reactions. The proteins are folded into a very particular shape, and this allows them to bind efficiently to the molecules of interest. At low temperatures, between 32 and 50 degrees Fahrenheit – 0 and 10 degrees Celsius – the enzymes that carry out photosynthesis do not work efficiently, and this decreases the photosynthetic rate. At medium temperatures, between 50 and 68 degrees Fahrenheit, or 10 and 20 degrees Celsius, the photosynthetic enzymes work at their optimum levels, so photosynthesis rates gauge high. t temperatures above 68 degrees Fahrenheit, or 20 degrees Celsius, the rate of photosynthesis decreases because the enzymes do not work as efficiently at this temperature. This must have been the reason for which scientists kept the temperature of the leaves at 20°C while they recorded results. (ii) Percentage change can be calculated by the formula: ∣V1​∣(V2​−V1​)​×100  where, V1​ is the initial value andV2​ is the changed value.In the given figure the initial value of  rate of photosynthesis at a light intensity of 1250 arbitrary units when the carbon dioxide concentration was140ppm is between 20-25, that is 23 and the changed value when the carbon dioxide concentration was increased from 140ppm to 1000ppm is 40.So, by taking the value of V1​= 23 and V2​= 40, we get=∣23∣(40−23)​×100 =2317​×100 =0.73913×100 =73.913% change . So we can conclude that there is an 73.913% = 74% (Rounding off to the nearest whole number) increase or change in the rate of photosynthesis is observed. (iii) From the given graph we can observe that the rate of photosynthesis increases with an increase in light intensity when the concentration of carbon dioxide was 140 ppm. After reaching to a certain optimum rate the rate of photosynthesis becomes constant at 1750 (a.u)/ 25µmol per m2 per s.(iv) Increasing the light intensity increases the rate of photosynthesis , until some other factor - a limiting factor - becomes in short supply. Other factors like amount of chlorophyll pigments, water, temperature and carbon dioxide are involved in photosynthesis. When  the concentration of carbon dioxide was 1000 ppm, light intensity acts as a limiting factor as the rate of photosynthesis does not level off even at high light intensities. Light is absorbed by chlorophyll and at very high light intensity, chlorophyll may be damaged and the rate drops steeply.

Question 19

Mammals have a double circulation.State what is meant by the term double circulation. ...................................................................................................................................................

Accepted Answer

Double circulation is the most efficient way of circulation found in all mammals. In this system, the blood flows through the heart twice. It is called a double circulatory system because blood passes through the heart twice per circuit. The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart. The left pump sends the newly oxygenated blood around the body.

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