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Biology Topic 6 - Plant Structures & Their Functions (During…
Biology Topic 6 - Plant Structures & Their Functions
During photosynthesis, photosynthetic organisms (e.g green plants, algae) use energy from the Sun to make glucose.
Some of the glucose is used to make larger, complex molecules that the plants need to grow. These make up organism's biomass.
Energy stored in the organism's biomass works its way through the food chain as animals eat them and each other.
Photosynthetic organisms are the main producers of food.
Photosynthesis happens inside chloroplasts as they contain chlorophyll which absorbs light. Energy is transferred to the chloroplasts by light.
Photosynthesis equation: Carbon dioxide + Water --(Light/Chlorophyll)--> glucose + oxygen
6CO^2 + 6H^2O --(Light/Chlorophyll)-->C^6^H^12O^6 + 6O^2
Biomass - The mass of living material.
Not enough light slows down rate of photosynthesis.
Light transfers energy needed for photosynthesis. AS light level is raised, rate of photosynthesis increases. But only up to a certain point after it won't make any difference.
Rate is directly proportional to light intensity.
Distance from lamp and light intensity are inversely proportional. So, as distance increases, light intensity decreases. Light intensity decreases in proportion to the square of the distance.
This means if you halve the distance, the light intensity will be four times greater. If you double the distance, light intensity is four times smaller.
Investigating the effect of light intensity of photosynthesis (Practical)
Canadian pond weed can be used to measure effect of light intensity on rate of photosynthesis. The rate it produces oxygen is the rate at which it's photosynthesising.
The faster the rate of oxygen production, faster the rate of photosynthesis.
- Apparatus is set up like this
First, the gas syringe should be empty. Sodium hydrogen carbonate may be added to water to make sure plant has enough CO^2.
A source of white light is placed at a specific distance from pond weed.
The pond weed is left to photosynthesise for a set amount of time.
As it photosynthesises, oxygen releases will collect in the gas syringe. Allows you to accurately measure volume of oxygen produced.
Repeat again with the light source at different distances away from pond weed.
Rate of oxygen production = volume produced / Time taken
Any variables that could affect results should be controlled. e.g Temperature controlled by putting conical flask in water bath. Also, CO^2 concentration can be controlled by adding set amount of sodium hydro carbonate to set volume of water.
Sodium hydrogen carbonate releases CO^2 in solution.
Too little CO^2 slows it down.
Increasing CO^2 concentration increases rate of photosynthesis up to a point. Aftter it flattens out. No longer being a limiting factor.
Temperature has to be just right. If temperature is the limiting factor it's because it's too low - enzymes needed for photosynthesis work more slowly at low temperatures.
However, if plant gets too hot the enzymes will denature. This happens at about 45C
Root hairs take in minerals and water.
Cells on the surface of plant roots grow into "hairs", they stick out into the soil. Each branch of a root is covered in millions of these hairs. This gives plants a large surface area for absorbing water and mineral ions from soil
Concentration of mineral ions is higher in root hair cells than soil around them, so mineral ions are absorbed by active transport. Water is absorbed by osmosis.
Phloem tubes transport food.
They're made up of columns of elongated living cells with small pores in the end walls to allow stuff to flow through.
They transport food substances (mainly sucrose) made in the leaves to the rest of the plant for storage or immediate use (in growing regions)
This is called translocation and it requires energy from respiration. Transport goes in both directions
Xylem Tubes take water up.
Xylem tubes are made of dead cells joined end to end with no end walls between them and a hole down the middle. Strengthened with a material called lignin.
They carry water and mineral ions from roots to stem and leaves.
The movement of water from the roots, through the xylem and out of the leaves is called transpiration stream.
