AQA A2 Biology B14 Stimuli Kerboodle Answers

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14.1 Survival and response AQA A2 Biology B14 Stimuli Kerboodle Answers: Page No. 63

1 Negative chemotaxis. 2 Positive chemotaxis. 3 Negative gravitropism.

14.2 Plant growth factors AQA A2 Biology B14 Stimuli Kerboodle Answers : Page No. 67

1 Cells in the tip of the shoot produce IAA, which is then transported down the shoot. The IAA is initially transported evenly throughout all regions as it begins to move down the shoot. Light causes the movement of IAA from light side to the shaded side of the shoot. A greater concentration of IAA builds up on the shaded side of the shoot than on the light side. As IAA causes elongation of shoot cells and there is greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more. The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light. And light used for photosynthesis. 2 It anchors plant firmly. It brings closer to water. 3 IAA is the universal natural auxin and cannot be easily made synthetically. IAA is naturally occurring in plants so no need of absorption. Not easily broken down and store in tip of root and shoot. They are not lethal to some plants in low concentration.

14.4 Receptors AQA A2 Biology B14 Stimuli Kerboodle Answers : Page No. 75

1 A special type of sodium channel which changes its permeability to sodium when it is stretched. 2 1. Pressure on pacinian corpuscle.

2. Corpuscle changes shape.
3. Stretches membrane of neurone.
4. Widens stretch mediated sodium channels.
5. Allows sodium ions into neurone.
6. Changes potential of membrane.
7. Produces generator potential.

3 Because only rod cells are stimulated by low-intensity light and rod cells cannot distinguish between different wavelengths. So object only perceived as black/white. 4 Because low intensity so cone cells not stimulated, which are situated on fovea and looking to one side means light is focused on periphery of retina where there are mostly rod cells which are stimulated by low intensity light.

14.5 Control of heart rateAQA A2 Biology B14 Stimuli Kerboodle Answers: Page No. 79

1 Controls the involuntary activities of internal muscles and glands. 2 Sympathetic stimulates effectors so speeds up an activity. Parasympathetic inhibits effectors and slows down an activity. 3 Remains high because the parasympathetic system is unable to transmit nerve impulses to the SA node, which decreases heart rate so lowers blood pressure. 4 Heart rate remains as it was before exercise because no nerve impulse can be sent to the centres that control heart rate. b Blood CO2 increases as a result of increased respiration during exercise. Banner 2

Practice questions: Chapter 14: Page No. 80-81

1 (a) Diffusion. (b) (i)

1. Causes plant to bend/grow towards light / positive phototropism;
2. (Light) required for photosynthesis.

(ii) r = 0.98 Value of r exceeds the critical value. So p < 5% of the correlation being chance. There is a genuine positive correlation. (iii) Value of r exceeds the critical value; So p < 5% of the correlation being chance; There is a genuine positive correlation (iv) They sprayed a solution containing NAA on the upper and lower surfaces of a leaf. The graph shows their results. (c)

1. More kinetic energy.
2. Faster movement of molecules.
3. More diffusion.

(d) (i) 1. Thick cuticle on upper surface / thin cuticle on lower surface / few stomata on upper surface / no stomata on upper surface;

2. More diffusion / shorter diffusion pathway (on lower surface).

(ii) Different species have different (qualified) properties. 2 (a) Three changes described e.g.,

1. Formation/growth of vacuole.
2. Formation of starch grains/amyloplasts.
3. Movement of grains/amyloplasts towards bottom of cell.
4. Cells get longer/wider/larger.

(b)

1. Grows sideways before starch grains form;
2. Bending starts when/as grains form;
3. More bending as grains increase in number;
4. More elongation (of cells)/growth (of roots) downwards as starch grains increase/move;
5. Bending starts before grains move down;
6. Could be related to vacuole;

(c) 1. Greater (elongation) growth on top of root/less growth on bottom of root;

2. (IAA) at bottom of root/where IAA concentration high inhibits expansion/elongation (of cells);
3. (IAA) at top of root/where IAA concentration low leads to expansion/elongation (of cells);

3 (a) 1. Membrane more permeable to potassium ions and less permeable to sodium ions.

2. Sodium ions actively transported/pumped out and potassium ions in.

(b) Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode P. (3 marks)

1. (Pressure causes) membrane/lamellae to become deformed/stretched;
2. Sodium ion channels in membrane open and sodium ions move in.
3. Greater pressure more channels open/sodium ions enter;

(c) 1. Threshold has been reached;

2. (Threshold or above) causes maximal response / all or nothing principle.

(d) 1. Less/no saltatory conduction / action potential/impulse unable to ‘jump’ from node to node;

2. More depolarisation over length/area of Membranes.

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Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it. References: BBC Bitesize AQA GCSE Science Kerboodle textbook Wikipedia Wikimedia Commons Join Our Free Facebook Group : Get A* in GCSE and A LEVEL Science and Maths by Mahima Laroyia: https://www.facebook.com/groups/expertguidance.co.uk/ For Free Tips, advice and Maths and Science Help Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it. References: BBC Bitesize AQA GCSE Science Kerboodle textbook Wikipedia Wikimedia Commons Join Our Free Facebook Group : Get A* in GCSE and A LEVEL Science and Maths by Mahima Laroyia: https://www.facebook.com/groups/expertguidance.co.uk/ For Free Tips, advice and Maths and Science Help