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Flashcards · 5090 · Topic 6

Plant nutrition flashcards

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Topic 6: Plant nutrition

Photosynthesis
The process by which plants make carbohydrates from raw materials using energy from light.
Word and balanced equations for photosynthesis
carbon dioxide + water → glucose + oxygen 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light energy and chlorophyll written by the arrow)
Chlorophyll
A green pigment found in chloroplasts. It transfers light energy into chemical energy for the formation of glucose and other carbohydrates.
Uses of starch, cellulose, glucose and sucrose in a plant
Starch: energy store. Cellulose: cell walls. Glucose: respiration. Sucrose: transport through the plant.
Testing a leaf for starch: steps and reasons
Boil in water (kills cells, breaks membranes); hot ethanol in a water bath, no naked flame (removes chlorophyll); warm water (softens the leaf); iodine on a white tile (blue-black = starch).
Why is a plant destarched before a photosynthesis experiment?
Keeping it in the dark uses up stored starch, so any starch found later was made during the experiment.
Limiting factor
The factor in shortest supply that keeps the rate of photosynthesis down. Only increasing this factor raises the rate.
Effect of temperature on the rate of photosynthesis
Rises to an optimum, then falls sharply: up to the optimum, more kinetic energy gives more effective collisions; above it, enzymes are denatured.
Hydrogencarbonate indicator around pondweed: yellow, red, purple
Yellow: more CO₂ than air (respiration greater than photosynthesis, e.g. dark). Red: same as air (the two balance). Magenta to purple: less CO₂ than air (photosynthesis greater, bright light).
Palisade vs spongy mesophyll
Palisade: tightly packed, near the upper surface, most chloroplasts, for photosynthesis. Spongy: loosely packed, fewer chloroplasts, air spaces giving a large surface for gas exchange.
Why is a leaf large and thin?
Large surface area absorbs more light and lets more carbon dioxide in. Thin: short diffusion distance for gases, and light reaches all the mesophyll cells.
Why plants need nitrate and magnesium ions
Nitrate: nitrogen to make amino acids, then proteins for growth. Magnesium: to make chlorophyll; less chlorophyll means less light absorbed.

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