MARKING SCHEME - HALF-YEARLY EXAMS 2016/2017

Transcription

1 S E C O N D A R Y S C H O O L M R I E H E L ST THOMAS MORE COLLEGE SECONDARY SCHOOL ZEJTUN MARKING SCHEME - HALF-YEARLY EXAMS 2016/2017 FORM: 3 Biology Time: 2hrs NOTE: / indicates alternative answers. Answers are an indication of what is acceptable. Accept other correct answers not indicated below after checking with other examiners. Section A: Answer ALL questions in the space provided. This section carries a total of 55 marks. 1. The frog is considered to be a living organism since it performs all the characteristics of life. Complete the table below showing the characteristics of life of the frog. Characteristic of Life Nutrition / feeding Reproduction Definition Eat insects that are necessary for growth and build-up of energy; Increase in number / to avoid extinction of the species Sensitivity / Irritability Movement Growth Hides under a stone in the presence of predators; Frogs use their back legs to push themselves when in the water; Increase in size / changing from tadpole into a frog Respiration Excretion Burning of food to build energy; Removal of waste after metabolism from the frog s body. Total 7 marks Biology F3 HY Page 1 of 14

2 2. The following diagram represents the human sex cells being studied in the laboratory. These cells are considered to be specialised cells. 1.3cm Cell A Cell B a) Write down the name of cells A and B Cell A: Sperm Cell B: Ovum/egg b) Explain the meaning of the term specialised. Special structure/shape Adapted to perform a special job/function c) What is the function of Cell A? To fertilise the female egg / ovum / gamete d) Name two other specialised cells found in the human body. Muscle cells/red blood cells / white blood cells / nerve cells / other examples e) Name the instrument used to study the above cells in the laboratory. Microscope f) The student wrote that Cell A has been magnified x250. Calculate the actual size of the part (shown above) that measures 1.3 cm. Show all your working. Actual Size = 1.3cm 250 = cm 1 mark working/1 mark correct answer/1 mark units (3) Total 11 marks Biology F3 HY Page 2 of 14

3 3. Plants use active transport to move some substances from the soil into the root. a) Explain the term active transport. Active Transport is the selective movement of molecules across living cell membranes using energy. b) Which organelle is expected to be present in abundance in root cells in order to ensure success of the process of active transport? Give a reason why. Organelle: Mitochondria Reason: Active transport needs energy / site of energy production / respiration c) Why is the process of active transport necessary in roots? To take up mineral salts against a concentration gradient / when in low concentrations d) Specialised cells, known as root hair cells, are present in roots. Draw a well labelled diagram of a root hair cell. 2 marks for correct diagram. ½ mark for ANY FOUR correct labels (4) e) How is the root hair cell adapted to perform its function? It has a long thin root hair that increases the surface area available for the absorption of water and minerals. Total 11 marks Biology F3 HY Page 3 of 14

4 4. a) Draw a typical animal cell and label all the structures that are normally found in it. Mitochondria (visible only under electron microscope) Nucleus (contains chromatin) Nuclear Membrane Vacuoles (food or contractile) Cell Membrane Cytoplasm Contains glycogen granules) 2 marks for correct diagram. ½ mark for ANY FOUR correct labels (4) b) Certain structures are found only in plant cells. List two such structures and give the function of each. Large Central Vacuole: It has a high pressure to keep the plant rigid and upright Chloroplasts: they carry out photosynthesis in the presence of sunlight Cellulose Cell Wall: gives the plant its stiffness and helps it grow tall / protective Starch granules: Storage molecules in cytoplasm of plant cells. (ANY TWO) (4) Total 8 marks Biology F3 HY Page 4 of 14

5 5. Many flowering plants can reproduce both sexually and asexually. a) Define the term asexual reproduction. Reproduction involving a cell dividing into two or more individuals / offspring Does not involve sex cells / gametes / Involving only a single parent (ANY TWO) b) State one advantage and one disadvantage of asexual reproduction for flowering plants. Asexual Reproduction Advantage Disadvantage Good characteristics are passed on / Much quicker than sexual reproduction / larger number of offspring (ANY ONE) No variation in offspring c) Potatoes can reproduce asexually by means of tubers. This can be observed in the following diagram: Soft and shrivelled tuber Explain why the tuber becomes soft and shrivelled when a new plant grows from it. New plant needs energy and chemicals to grow. It obtains these from the starch stored in the tuber / used for respiration and growth Total 6 marks Biology F3 HY Page 5 of 14

6 6. Biology students investigated the effect of size of organisms on diffusion of molecules. For the purpose of this investigation, the organisms were represented by cubes made of transparent gelatine jelly. They cut 2 cubes as follows: Cube A Sides 3 cm each Cube B Sides 1 cm each a) Calculate the Surface Area to Volume ratio for each of the above cubes. Show your working. Cube A Cube B Surface Area (3 x 3) x 6 = 54cm 2 (1 x 1) x 6 = 6cm 2 Volume 3 x 3 x 3 = 27cm 3 1 x 1 x 1 = 1cm 3 SA:Volume ratio 54 : 27 2:1 6 : 1 b) After preparing the cubes, they placed each one of them in a beaker filled with redcoloured water. They left the cubes in the beaker for 15 minutes. After removal from the beaker, the students cut through the centre of each cube and observed the diffusion of the red-coloured water into the cubes. i) Explain the term diffusion Diffusion is the movement of particles from a region of high concentration to (6) a region of low concentration until they are spread out evenly Biology F3 HY Page 6 of 14

7 ii) In which cube do you expect the red colour to diffuse faster? Explain your answer. Cube B It has a larger surface area to volume ratio / more surface area per unit volume iii) Write down one precaution the students should have followed during this investigation. Same temperature of coloured water / cubes made from same jelly (ANY ONE) (1,1) iv) Write down one advantage organisms represented by Cube B could have over organisms represented by Cube A. Cube B organisms would lose heat more easily in hot conditions / can carry out gaseous exchange more easily / can absorb nutrients more easily (ANY ONE) Total 12 marks Section B: Answer question ONE and ANY OTHER TWO questions on the papers provided. This section carries a total of 45 marks. 1. Germination is a process, controlled by enzymes, in which the seed begins to develop into a new young plant. Three main factors are needed for successful germination. Germination of seeds may be either hypogeal or epigeal. Biology students investigated the changes in dry mass of pea seeds as they germinated and grew into new plants. Before planting them, they allowed the seeds to soak in water for 24 hours. The planted seeds were left on a window sill for 12 days, and the dry mass of the whole germinating plant, including the seed, was measured every 2 days. The following table shows their results over a 12-day period. Time (days) Dry mass of germinating plants (g) Biology F3 HY Page 7 of 14

8 Dry mass of germinating plants (g) a) Plot a graph of dry mass of germinating plants (y-axis) against time (x-axis) (5) Dry mass of germinating plants (g) against time (days) Time (days) Correct plotting Correct use of scales / graph Title Labels Deduct ½ mark if units are not included b) Explain why there was a decrease in the dry mass of the germinating plants during the first 6 days. Food store in seed was being used up for growth and energy. c) Why were the seeds soaked in water for 24 hours before planting them? Activates enzymes need for growth / helps to convert starch to sugar and proteins to amino acids / expands vacuoles of newly formed cells (so that root, shoot and leaves can expand) / maintains turgor in the growing cells. (ANY ONE) d) Besides water, list two other important factors needed for successful germination. Oxygen / Temperature e) The students found that hypogeal germination is characteristic of pea seeds. Explain the term hypogeal. Cotyledons / Seed leaves remain beneath ground while shoot grows out of soil f) List two things that the students should have kept the same when carrying out the investigation to ensure accurate results. Same type of seed / Same type and depth of soil / same spacing of seeds / same depth in soil (ANY TWO) g) At the end of the investigation, one of the students said that if they repeated the experiment by placing the planted seeds in a dark cupboard, no growth would be observed. Is the student correct? Explain your answer. Incorrect Most seeds will germinate anyway, and they will grow taller once they sprout in order to find light Total 15 marks Biology F3 HY Page 8 of 14

9 2. Seed dispersal is the movement or transport of seeds, usually far away from the parent plant. Plants have very limited mobility and so depend on a variety of dispersal methods to transport their seeds. a) The following are seeds taken from a variety of plants. For each one state the dispersal method. G0zT03GSTlE/Uqwft7cUBVI/AAAAAAAACfc/ p_ktjb25pf0/s1600/seeds+dispersal+by+animals+vs+by+wind.png A B C D (4) A = Mechanical / explosive dispersal B = Animal dispersal C = Animal dispersal D = Wind dispersal b) During dispersal, seeds are usually carried far away from the parent plant. List two advantages of this process. They do not compete with parent plant / Spread out / colonise new areas (ANY TWO) Biology F3 HY Page 9 of 14

10 c) Draw a well-labelled diagram of a typical seed you have studied. (4) 2 marks for correct diagram / 2 marks for any 4 labels. Accept also any other suitable seed d) Seeds have the ability to remain dormant. Explain the advantage of this. They can survive for a long time until conditions are favourable. e) Seeds develop from ovules. Name the structure a true fruit develops from. Ovary. f) The strawberry is considered to be a false fruit. Explain this term. Fleshy part of fruit develops from the receptacle. Seeds / pips are formed from ovaries. Total 15 marks 3. John, a biology student, wanted to investigate the effect of osmosis on the size of potato cubes. He cut 3 potato cubes, all of the exact size, weighed them and placed them in boiling tubes with different solutions. He left them for 30 minutes, removed them, and weighed them once more. The following table shows the results obtained: Cube Original Weight (g) Final weight (g) % Change A % B C ? Biology F3 HY Page 10 of 14

11 a) Explain the term osmosis. Osmosis is the movement of water molecules across a semi-permeable membrane from a dilute (weak) solution to a concentrated (strong) solution. DO NOT accept from a high concentration to a low concentration unless water molecules are specified. b) Calculate the % Change of cube C. Show all your working. (3) Difference in weight: = Percentage change: x 100 = - 56% Deduct 1 mark if answer is not negative / not described as a decrease. c) Explain why cube B showed no change in size. The solution and the cell contents / cytoplasm / cell vacuoles must have been isotonic / the same concentration / equal concentration. d) Draw a diagram to explain the state of the potato cells found in cube C. Central vacuole Shrinks as it loses water Cell membrane moves away from cell wall e) Suggest why John cut the potato cubes to exactly the same size. Different surface area to volume ratio leads to different rate of osmosis / to ensure that the rate of osmosis will be the same. f) Name the biological terms used to describe the state of cube A and the state of cube C Cell A is Turgid Cell C is Flaccid g) While researching the topic, John read that in hospital, patients are never given drips (liquid that enters directly into the blood) consisting of pure water. Explain why. Cytoplasm of red blood cells is more concentrated than pure water Water uptake by osmosis Red blood cells burst. (3) Total 15 marks Biology F3 HY Page 11 of 14

12 4. Give a biological explanation for each of the following statements: a) It is incorrect to say that respiration and breathing are the same thing (4) Respiration refers to burning of food for energy in cells Gaseous exchange refers to intake and removal of O2 and CO2 by organism/cell b) Salad lettuce can be made more crisp by placing it in a bowl of water (3) Contents of cells are more concentrated than surrounding water Water enters cells by osmosis Lettuce cells become turgid, making lettuce crisper c) One cannot observe mitochondria with a light microscope Mitochondria are very small structures Magnification power of light microscopes is not enough to make them visible / only electron microscopes have enough magnification to see them. d) Diffusion and osmosis are both passive processes but different from each other. (3) Passive = they do not use energy from the organism Osmosis refers only to water / involves semi-permeable membrane Diffusion refers to all other molecules / does not need a semi-permeable membrane e) An onion is part of a plant but is not green (3) Not green since it does not have any chloroplast It is an underground storage organ Does not carry out photosynthesis Total 15 marks 5. The flowers of wind-pollinated flowers, such as the Ryegrass, are less colourful than the flowers of insect-pollinated flowers. The following image shows the flower of the Ryegrass. Biology F3 HY Page 12 of 14

13 a) Why are wind-pollinated flowers less colourful than insect-pollinated flowers? Do not need to attract insects b) From the above image, list two characteristics that show that the Ryegrass is wind-pollinated. Stigma has feathery branches for catching pollen / Stamens and stigma hang out of the petals / Stamens have limp filaments (ANY TWO) c) Both wind and insect-pollinated flowers produce pollen. Pollen is the male reproductive cell. List two ways of how pollen produced by wind-pollinated flowers is different from that produced by insect-pollinated flowers. Wind - Large number of pollen grains produced / Pollen grains very light / not sticky / smooth. (ANY TWO) Insect - Small number of pollen grains produced / Pollen grains heavier / sticky. (ANY MATCHING TWO) d) Besides producing pollen, insect-pollinated flowers also produce nectar. Why is this important? Nectar is a sugary solution that attracts insects / Insects attracted to nectar. e) Draw a large diagram of an insect-pollinated flower. On the diagram label only the different parts of the male and female reproductive structures. (4) Stigma Anther Carpel Style Filament Stamen Ovary ½ mark for each correct label (2.5 marks) 2 ½ marks for diagram f) Most plants use cross-pollination, however there are a number of plants, such as the peanuts, that perform self-pollination. i) Explain the term cross-pollination? Pollen from one flower fertilizes ovary of a different plant. ii) Why is cross-pollination considered to be better than self-pollination? It results in variation due to mixture between different flowers / individuals iii) List a situation when self-pollination may be of an advantage to the plant. Biology F3 HY Page 13 of 14

14 If a flower is not cross-pollinated, self-pollination will result in the production of fruits / seeds anyway. g) Describe what happens from the time of pollination to the time fertilisation takes place. The pollen grain absorbs liquid from stigma. (½) A microscopic pollen tube grows down from pollen grain into the ovule. (½) The nucleus of pollen grain travels down pollen tube and enters ovule. (½) It fuses with nucleus of egg cell. (½) Total 15 marks Biology F3 HY Page 14 of 14