Topic 6 : Plant Structures and Their Functions Flashcards
What are photosynthetic organisms?
They are producers that make their own food and are the main source of biomass.
What type of reaction is photosynthesis and what does it produce?
It’s an endothermic reaction that uses light energy to turn carbon dioxide and water into glucose and oxygen.
What are the three main limiting factors of photosynthesis?
Temperature, light intensity, and carbon dioxide concentration.
How does temperature affect photosynthesis?
It increases the rate up to an optimum, but too high a temperature denatures enzymes and slows the reaction.
How does light intensity affect photosynthesis?
Higher light intensity increases the rate until another factor becomes limiting.
How does carbon dioxide concentration affect photosynthesis?
More CO₂ increases the rate until it levels off due to another limiting factor.
How do the three limiting factors interact?
The rate of photosynthesis is limited by whichever factor is in shortest supply.
How can you investigate the effect of light intensity on photosynthesis?
Measure the rate of oxygen bubbles produced by pondweed at different distances from a light source.
What is the inverse square law for light intensity?
Light intensity ∝ 1 ÷ distance² — as distance increases, light intensity decreases rapidly.
How is a root hair cell adapted for absorption?
It has a large surface area and thin walls to absorb water and minerals efficiently.
How is xylem adapted for its function?
Made of dead, lignified cells that form tubes to carry water and minerals upward.
How is phloem adapted for its function?
Made of living cells with companion cells that use energy to transport sucrose around the plant.
How are water and minerals transported in a plant?
Through the xylem by transpiration — water evaporates from stomata, pulling more up.
What controls water loss through the stomata?
Guard cells open and close stomata to regulate water loss and gas exchange.
How is sucrose transported in plants?
By translocation in the phloem, from sources (leaves) to sinks (roots or growing areas).
How is a leaf adapted for photosynthesis?
It has a large surface area, thin structure, chloroplasts, and many stomata for gas exchange.
What environmental factors affect water uptake?
Light intensity, air movement, and temperature increase transpiration and water uptake.
How can you calculate the rate of transpiration?
Measure water loss over time using a potometer.
How are plants adapted to extreme environments?
Features include small leaves, thick cuticles, sunken stomata, and water storage tissues.
What are auxins and what do they do?
Plant hormones that control growth and direct roots and shoots to grow towards or away from stimuli.
What are phototropism and gravitropism?
Growth towards light (phototropism) and growth in response to gravity (gravitropism), both controlled by auxins.
How are auxins used commercially?
In weedkillers to kill broadleaf plants and in rooting powders to grow new plants.
What are gibberellins used for commercially?
To promote seed germination, flower and fruit development, and produce seedless fruit.
What does ethene do in plants?
It controls fruit ripening and is used commercially to ripen fruit during transport.
