(a) A student investigated the conditions needed for the germination of cress seeds. Fig. 5.1 shows the apparatus, conditions used and the results of the investigation.
(i) Identify the letters of the two test‑tubes in Fig. 5.1 that show that oxygen is needed for germination ………… and ………… .
(ii) A gardener wanted to store some cress seeds for a long time before using them. Use the information in Fig. 5.1 to identify the ideal conditions to prevent germination. Tick two boxes
(b) Tropic responses were investigated in two plants, X and Y. The plants were placed in separate boxes for 5 days. Fig. 5.2 shows plants X and Y at the start of the investigation. Both boxes had a hole on one side that let light in. Plant X was kept in the same position. Plant Y was placed on a platform that was continually rotated.
(i) Predict and explain how the shape of plant Y will differ from the shape of plant X after 5 days of growth.
(ii) State the name of the tropic response that would be seen in plant X in Fig. 5.2 after 5 days.
(iii) Suggest and explain the advantage to a plant of tropic responses in shoots.
(c) State the position plants occupy in a food chain.
▶️ Answer/Explanation
Ans:
(a)(i) C ; D / E
Test-tubes C and D/E show that oxygen is needed for germination. In C, seeds are submerged in boiled water (no oxygen), and in D/E, oxygen is absent due to displacement by another gas or vacuum.
(a)(ii) cold ticked ; dry ticked
Cold and dry conditions inhibit germination by slowing metabolic activity and preventing water absorption, respectively.
(b)(i) plant Y would be straight(er) ; all, sides / parts / leaves, of plant Y, receives light
Since Plant Y is rotated, light exposure is even on all sides, preventing directional growth (tropism).
(b)(ii) phototropism
Plant X grows toward the light due to phototropism, a directional response to light.
(b)(iii) receives more light / AW ; for photosynthesis
Tropic responses help shoots maximize light absorption, enhancing photosynthesis and growth.
(c) first trophic level / producer
Plants are producers, forming the base of the food chain by converting sunlight into energy.
A seedling is a seed which has just started to grow a small root and a small shoot.
(a) State the environmental conditions that a seed requires to grow into a seedling.
(b) Fig. 6.1 shows a drawing of a seedling at the start of an investigation into plant growth responses.
The seedling was attached to a piece of card so that the root and shoot were horizontal.
The card and seedling were placed inside a box that excluded all light. The box was placed on the ground for three days.
Fig. 6.1 shows the apparatus at the start of the investigation.
(i) On Fig. 6.2 draw the expected appearance of the root and shoot after three days in the box.
(ii) State the name of the response shown by the root and the shoot in this investigation.
▶️ Answer/Explanation
(a) Water; oxygen; suitable temperature; space (or any other valid condition).
Explanation: Seeds require specific environmental conditions to germinate and grow into seedlings. Water is essential to activate enzymes that break down stored food in the seed. Oxygen is needed for aerobic respiration to provide energy for growth. A suitable temperature is necessary as it affects enzyme activity – too cold and reactions slow down, too hot and enzymes may denature. Space allows for root and shoot expansion and access to resources.
(b)(i)
Expected drawing: root pointing down, shoot pointing up
Explanation: After three days in the dark box, the root would grow downward (positive gravitropism) and the shoot would grow upward (negative gravitropism). This occurs because plant roots are positively gravitropic – they grow in the direction of gravity, while shoots are negatively gravitropic – they grow against gravity. This response ensures the root grows into the soil to absorb water and minerals, while the shoot grows upward to reach light for photosynthesis.
(b)(ii) Tropism (or specifically gravitropism/geotropism).
Explanation: The response shown by both the root and shoot is called tropism, which is a growth response to directional external stimuli. In this case, it’s specifically gravitropism (also called geotropism) as the response is to gravity. The root shows positive gravitropism (growing with gravity) while the shoot shows negative gravitropism (growing against gravity). This differential growth response is controlled by the distribution of auxins (plant hormones) in response to gravity.