Andy Todd

thebiotutor.com

2I Excretion

Time: 1 hour 6 minutes

Total marks available: 66

Total marks achieved: ______

Andy Todd

Q1.

One of the characteristics of living organisms is the ability to respond to a change in their surroundings. In mammals, such as humans, responses are controlled by nervous or hormonal communication.

(a) ADH is an example of a hormone. (i) Where is ADH produced?

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.............................................................................................................................................. (ii) Describe the effects of ADH in the body.

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(b) Describe two ways in which nervous communication differs from hormonal communication.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) Plants are also able to respond to their surroundings. The diagram shows young cereal shoots (coleoptiles) which are placed in different light conditions.

Complete the diagram to suggest how each of the shoots would appear after two days. (3)

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(d) Plant roots also respond to external stimuli.

Describe the response of roots to gravity and explain how this response benefits the plant.

(3)

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(Total for question = 12 marks)

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Q2. (a) The table lists some structures that provide a large surface area for the diffusion of substances. Complete the table by naming the organ in which each structure is found. The first one has been done for you.

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(b) What is meant by the term diffusion?

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(c) The nephron is involved in the removal of substances from the blood.

Describe how substances are removed from the blood into the nephron. (2)

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(Total for question = 7 marks)

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Q3.

The skin is an organ of homeostasis and excretion.

(a) Describe what is meant by the term excretion. (2)

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(b) The diagram shows a section through the skin with two structures labelled A and B.

The structures labelled A and B play a part in homeostasis when a person enters a very warm environment.

(i) Explain the role of structure A. This text is an indented paragraph that lines up with the text after the "i)".

(3)

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(ii) Explain the role of structure B.

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(c) Some hormones are involved in homeostasis.

(i) Explain the role of insulin in homeostasis. (2)

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(ii) Explain the role of ADH in homeostasis.

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(Total for question = 13 marks)

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Q4.

The human kidney removes urea from the blood.

(a) Name two other substances the kidney removes from the blood. (2)

.............................................................................................................................................. .............................................................................................................................................. (b) The diagram shows a simple kidney machine that uses dialysis to remove urea from the blood.

Dialysis allows small molecules to be removed from the blood. This is done by passing the dialysis solution over the tube containing the blood. The small molecules move from a region of high concentration to a region of low concentration.

(i) Give one way in which dialysis is similar to diffusion. (1)

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(ii) Give one way in which dialysis is similar to osmosis.

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(iii) Describe how the kidney machine removes urea from the blood.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (iv) Another function of the kidney machine is to maintain normal blood glucose concentration. Suggest how the concentration of glucose in the dialysis solution helps to maintain a normal glucose concentration in the blood.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (v) Describe two processes that take place in the kidney but not in the kidney machine.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) Kidney failure can be treated by transplanting a healthy donor kidney into the patient. (i) The procedure involves connecting two blood vessels and a tube to the transplanted kidney. Name the two blood vessels and the tube.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) Suggest why the transplanted kidney is placed in the lower abdomen instead of in the kidney's usual location.

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(Total for question = 16 marks)

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Q5.

The diagram shows some of the blood vessels and a nephron in the human kidney. The numbers represent the concentration of glucose at various places in the blood vessels and in the nephron, in arbitrary units.

(a) Explain how the structure of the blood vessels entering and leaving the glomerulus help to move glucose into the Bowman's capsule.

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(b) What type of blood vessels are found in the glomerulus?

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.............................................................................................................................................. (c) (i) Describe how glucose is reabsorbed from the nephron back into the blood.

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.............................................................................................................................................. (ii) Suggest why glucose needs to be returned to the blood.

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(Total for question = 7 marks)

Andy Todd

Q6.

(a) The diagram shows a section through a leaf.

(i) Name the structures labelled A and B.

(2) A .................................................................................................................................................................................................... B ....................................................................................................................................................................................................

(ii) Give the function of the waxy cuticle.

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.............................................................................................................................................. .............................................................................................................................................. (iii) Some of the leaf cells carry out photosynthesis. Write a word equation for this process.

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.............................................................................................................................................. (iv) Plants, like all living organisms, need to excrete waste products. Explain how the excretory product of photosynthesis is removed from the leaf.

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.............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (b) Some plants lose their leaves in cooler months. This can be described as an excretory mechanism. Suggest two other reasons why some plants lose their leaves in cooler months.

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.............................................................................................................................................. (c) Name one excretory organ in humans and name the substance it excretes.

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substance

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(Total for question = 11 marks) Q1. In this question candidates needed to recall where ADH is produced. Most candidates stated the pituitary glands and some the hypothalamus. On this occasion at International GCSE we were prepared to accept the site of release and the site of production. In part (a) (ii) candidates had to describe the effects of ADH on the body. The best responses described how ADH increases the permeability of the collecting duct wall. This leads to more water being reabsorbed into the blood by osmosis resulting in a smaller volume of more concentrated urine being released. Some candidates tried to describe the effect of less ADH and generally confused themselves. In part (b) most could recall two differences between nervous and hormonal communication. In part (c) candidates had to predict the outcome of an experiment on coleoptiles and light. Almost all could draw the correct response for the light from all around and most for unidirectional light few gained the mark for coleoptile in darkness. In (d) most candidates could describe the response of roots as positively geotropic and helping the plant by absorbing water and mineral ions. Fewer mentioned the role of the roots in anchoring the plant. Q2.

This question gave candidates a table of structures that provide a large surface area for diffusion. Almost all could identify the organs correctly. In part (b) most could describe diffusion as the movement of particles down a concentration gradient but less able candidates wrote about substances moving rather than ions, particles or molecules. In (c) the best responses included the movement of molecules from the glomerulus into the Bowman's capsule under pressure.

Q3.

For this question the better students are fully aware that excretion involves the removal of metabolic waste from the human body and gained full marks. Many gave named metabolic waste products and many confused excretion with egestion. Most appreciated that the labelled part A in the diagram of a skin section was a sweat gland. Marks were given for appreciating that released

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sweat will help the body lose heat when it evaporates. Weaker students struggled to interpret the diagram and wrote about part A as if it were a hair follicle or a receptor. Most recognised part B in the diagram and the best students gained all three marks by discussing the role of vasodilation allowing more blood to reach the skin surface and how this would help in cooling the body. Weaker students believed that the blood vessels move closer to the skin surface. Part (c) examined knowledge about the role of insulin. Students are encouraged to be precise with their language. Marks were given if students stated clearly that insulin reduces blood glucose by converting it to glygogen which is stored in the liver. Correct spelling of glycogen was essential as there were many answers where the term glucagon was used and examiners needed to be confident that the students knew the difference. The role of ADH in osmoregulation is well known by students. Marks were awarded for appreciating that ADH increases the permeability of the collecting duct so water can be reabsorbed into the blood.

Q4.

This question concerned the kidney and use of a dialysis machine. In part (a) most candidates could name one substance removed by the kidney. This question sought to examine the ability of students to apply biological principles to an unfamiliar context and therefore discriminated well between candidates. . In part (b) (i) and (ii) candidates had to give one way that dialysis is similar to diffusion and one way in which dialysis is similar to osmosis. Most could describe dialysis and diffusion as being down a concentration gradient and many could also recognise the presence of a partially permeable as being common to dialysis and osmosis. In part (iii) the better candidates could explain how urea is removed from the blood by diffusion down a concentration gradient and across a partially permeable membrane. In part (iv) only the candidates with higher levels of understanding could suggest how the concentration of glucose in the dialysis fluid maintains the blood glucose level. In part (v) the best responses could describe ultrafiltration and selective reabsorption as processes that occur in the kidney but not in the dialysis machine. Part (c) (i) asked candidates to recall the blood vessels and the tube that are connected to a kidney. Many could name the blood vessels but some confused urethra with ureter or attempted an amalgam of the two. Finally, in part (c) (ii) only the most able could suggest that the transplanted kidney is placed in the lower abdomen as the kidney will be nearer the bladder, the ureter and blood vessels can be shorter and access is easier.

Q5.

In this question only the best students were able to access part (a) of this question fully. Few recognised that the difference in the diameter of the afferent and efferent arterioles is responsible for the pressure needed for ultrafiltration, and many students gave irrelevant answers concerning capillary structure and diffusion. In part (b), most recalled that the blood vessels of the glomerulus are capillaries. In part (c), only the better students were able to gain full marks, no doubt understanding that the numbers on the diagram indicate the involvement of active transport. Most appreciated in part (d) the importance of glucose as a substrate for respiration.

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Q6.

This question provided a diagram of a section through a leaf. In part a) almost all candidates could correctly name the structures labelled. Most were able to give the function of the waxy cuticle as reducing transpiration and preventing entry of microorganisms. Most could also give the word equation for photosynthesis, although a significant minority chose to give chemical formulae. In the final part the better candidates gained full credit for explaining that oxygen exits the stomata down a diffusion gradient from a high concentration to a lower one outside the leaf. Part b) asked candidates to suggest reasons why some plants lose their leaves in cooler months. Answers that gained credit included reduction of water loss, lack of sunlight for photosynthesis and conservation of energy resources.

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