DSS 2019 Flashcards
Beetroot discs are immersed in 2 cm3 of sucrose solution from the test tube. A3fter 2 hours, a small drop is placed back into the original solution.
Explain why the drop of bathing solution rose in the 0.6 M solution. [4]
- The water potential of the cell sap in the beet root cells was higher than the 0.6 M sucrose solution. [1]
- Water moves out of the beet root cells into the 0.6 M bathing sucrose solution across the partially permeable cell membrane [1] by osmosis. [1]
- The bathing solution becomes less dense than the 0.6 M sucrose solution and floats [1]
State how meisis can result in variation in the lily, Lilium candidum. [2]
Crossing over occurs during prophase I. [1]
Random assortment occurs during metaphase I and II. [1]
The leaf shown in Fig. 4.1 has a number of adaptations to reduce water loss by transpiration. Two of the adaptations are:
x a multilayered epidermis x stomata only found in depressions, known as stomatal crypts, on the lower surface of the leaf.
Explain how the two adaptations will help to reduce water loss in N. oleander. [3]
1. multilayered epidermis
2. stomatal crypts
- multilayered epidermis reduces loss of water vapour /evaporation through the cuticle [1]
-
stomatal crypts The leaf has sunken stomata that lie in the grooves of the leaf on the lower surface of the leaf / has hairs that trap water vapour diffusing out of the stomata. [1]
This increases the humidity around the stomata and so reduces the rate of transpiration. [1]
Suggest three things that could happen to account for an increase in body temperature [2]
- exercise
- increase in temperature of the surroundings
- increase in metabolism/ increase in respiration
- fever
- ovulation
Explain why trophic level A is smaller than trophic level B in the pyramid of energy in
Fig. 7.1. [2]
- 90% of the energy at each trophic level is lost to the surroundings when energy is transferred from one trophic level to another. [1]
- Energy is lost to the surroundings in the form of heat/undigested materials/excretory products/uneaten body parts [1]
Define the term bioaccumulation. [2]
Bioaccumulation is the process by which certain chemicals are not excreted from the bodies of organisms but accumulate in their bodies. [1]
The chemicals are then passed along the food chains and become concentrated in the bodies of the final consumers. [1]
Describe how human activities are affecting the carbon cycle. [3]
The burning of fossil fuels releases carbon dioxide into the environment [1]
Deforestation reduces the removal of carbon dioxide from the atmosphere [1].
The decrease in the amount of carbon stored in carbon sinks increases the amount of carbon dioxide in the atmosphere [1]
Cockroaches are pests which damage food and spread diseases. They have a gene which makes them attracted to sugar. In the 1980s, a mixture of insecticides and sugar was used as a means of pest control. The sugar attracted the cockroaches and the insecticide killed them. In the 1990s, certain populations of cockroaches were no longer attracted to sugar. The insecticide was still lethal but the cockroaches avoided eating it when it was mixed with sugar.
Explain how the cockroaches evolved to survive the pest control used in the 1980s. [4]
The gene for sugar attraction was mutated [1] and led to variation/ populations individuals that are not attracted to sugar. [1]
Those that are not attracted to sugar did not eat the poison and survived. [1]
Those that survive have a higher chance of reproduction to pass on the genes to the next generation. [1]
Describe one difference between the process of artificial selection and natural selection.
Include reference to the production of one named economically important plant or animal
in your answer. [2]
- In natural selection, nature selects for the varieties that are better adapted to changes in the environment but in artificial selection humans select the varieties of organisms that suit their needs. [1]
- In natural selection, the varieties are produced by mutations but in artificial selection, the varieties are produced by selective breeding. [1]
Example, good meat-producing and milk-producing cattle
(accept any suitable example of an economically important plant or animal).
What are the advantages of genetic engineering over selective breeding? [4]
- Genes from any organism can be inserted into non-related species or different species. [1]
- Genes are carefully selected before transfer into an organism. This reduces the risk of genetic defects being passed on to the offspring. [1]
- Genetic engineering uses individual cells which reproduce rapidly in the laboratory in a small container. [1]
- More efficient. For example, transgenic salmon grow faster and require less food than ordinary salmon. [1]
Describe the double circulation of blood in the human circulatory system and the different
functions of the two circuits. [6]
- In the double circulation of blood, the blood passes through the heart twice in one complete circuit. [1]
- Double circulation in humans consists of the pulmonary circulation and systemic circulation. [1]
- In the pulmonary circulation the blood flows between the lungs and the heart [1]
- Pulmonary arteries carry deoxygenated blood from the heart to the lungs to be oxygenated [1]
- Pulmonary veins carry oxygenated blood from the lungs back to the heart [1]
- In the systemic circulation the blood is pumped/flows from the heart to the rest of the body and then back to the heart [1]
- Oxygenated blood leaves the aorta and is distributed by arteries to all parts of the body except the lungs. [1]
- Veins carry blood from all parts of the body back to the right side of the heart. [1]
Explain how the structure of capillaries is adapted for the transport of a named material to tissue fluid. [4]
- The walls of a capillaries is one cell thick. [1]
- The endothelium is partially permeable which enables certain substances to diffuse quickly though the capillary walls. [1]
- The narrow lumen of capillaries allows red blood cells to move through in a single
file [1] lowering the rate of blood flow and increasing the efficiency of exchange of
materials between the blood and the tissue cells. [1] - The dense network/repeated branching of capillaries increases the total cross-
sectional area. [1] The increase in total cross-sectional area lowers the blood pressure in capillaries, giving more time for the exchange of substances. [1] - Dissolved food substances/ oxygen [1] transported from the blood in the capillary across the capillary wall into the tissue fluid by diffusion. [1]
- Metabolic/excretory waste products from cells [1] diffuse into the tissue fluid and then through the capillary walls into the blood. [1]
(any 2 marks from structure of capilliary and 2 marks for a named material)
Explain why most living organisms depend on photosynthesis. [6]
- Plants convert light energy in the presence of carbon dioxide and chlorophyll into chemical energy in the form of glucose during photosynthesis [1] OR Plants are producers/ autotrophs unlike other living organisms [1]
- Excess glucose produced is converted into sucrose and transported to the storage organs whereby the sucrose is converted to starch [1].
- The glucose produced during photosynthesis can react with nitrates brought to the leaves to form amino acids which will be stored in the plants as proteins [1]
- The glucose produced can be converted to fats for storage. [1]
- Primary consumers or herbivores obtain their energy/ nutrients by consuming plants [1]
- Secondary consumers feed on the primary consumers for food thus depending indirectly on plants for food [1]
- Photosynthesis produces oxygen which organisms use when they undergo respiration to breakdown glucose in food to release energy [1]
(any 6 points)
Explain why increasing the light intensity in which a plant is growing does not necessarily increase its rate of photosynthesis. [4]
- There are other limiting factors such as temperature [1] and concentration of carbon dioxide [1]
- Temperature above and below the optimum temperature can affect the rate of photosynthesis as enzymes are involved [1]
- Insufficient carbon dioxide can affect the rate of photosynthesis as it is a raw material for photosynthesis [1]
