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a) The diagram shows a celery stem in some red dye - Edexcel - GCSE Biology - Question 4 - 2017 - Paper 1
Question 4
a) The diagram shows a celery stem in some red dye. The red dye moves up the celery stem. A student used five sets of this apparatus to study the rate of transpirat... show full transcript
Worked Solution & Example Answer:a) The diagram shows a celery stem in some red dye - Edexcel - GCSE Biology - Question 4 - 2017 - Paper 1
Step 1
Suggest how these five sets of apparatus could be used to measure the effect of light intensity on the rate of transpiration.
Answer
To measure the effect of light intensity on the rate of transpiration, the student can adjust the distance of a light source from each celery sample to vary the light intensity. For example, each of the five setups can have differing distances from a lamp (e.g., 10 cm, 20 cm, 30 cm, etc.). It is important to keep other factors constant, such as temperature and humidity, to ensure that the results reflect the effect of light intensity alone on transpiration rates.
Step 2
Explain why the rate of transpiration decreases between 25°C and 30°C.
Answer
The rate of transpiration decreases between 25°C and 30°C because at higher temperatures, the plant may experience water stress due to excessive evaporation and inadequate water uptake. As water loss increases, the stomata may close to prevent desiccation, which consequently reduces transpiration rates.
Step 3
Step 4
Explain one way in which root hair cells absorb mineral ions from the soil.
Answer
Root hair cells can absorb mineral ions from the soil through active transport. This process requires energy, as the cells move ions against their concentration gradient, allowing them to uptake essential minerals even when they are present in lower concentrations in the soil compared to within the root hair cells.
Step 5
Explain how water moves from root hair cells, across the root and into the stem.
Answer
Water moves from root hair cells through osmosis, as it travels from the high concentration of water in the root hair cells to lower concentrations in the surrounding root tissues. Once inside the root, water continues to move upwards through the xylem vessels by capillary action and transpiration pull, reaching the stem and eventually the leaves.