Plant Nutrition and Transport
Photosynthesis is the process that produces food in plants, it produces glucose.
Photosynthesis happens in the chloroplasts, which are found in leaf cells and in other green parts of a plant. Chloroplast contains a pigment called chlorophyll which absorbs sunlight and uses its energy to convert carbon dioxide and water to glucose. Oxygen is produced.
Leaves are designed for photosynthesis as seen by the structure:
- Leaves are broad so there is a large surface area exposed to light.
- Most of the chloroplasts are found in the palisade layer. That is so they’re near the top of the leaf where there is a lot of light.
- The palisade is very tightly packed so no light is lost.
- The upper epidermis is transparent so light can pass through.
- Leaves have a network of vascular bundles → they are transport vessels xylem and phloem. They deliver water and other nutrients to each part of the leaf and take away the glucose.
- The waxy cuticle stops water leaving by evaporation
- And the leaf is great at gas exchange as there is a lot of space in the spongy mesophyll where the gases i.e. CO2can be exchange.
Rate of Photosynthesis
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The three things that effect that rate of photosynthesis is CO2 and light intensity and Temperature, they can be limiting factors. A limiting factor is something that stops something for progressing i.e. if there isn’t any light no photosynthesis will happen. :
To test the leaf for starch:
- Leaf is killed in boiling water to stop all chemical reactions for fair test
- Put it in ethanol to rid of chlorophyll, it should turn white
- Then add iodine solution to test for starch.
We can use the starch test to test what affects the rate of photosynthesis by taking it away, i.e. by covering so it has no light or putting in a vacuum with soda lime so there is no CO2.
We can also see the photosynthesis through the rate of oxygen production by the plant and we can measure that by this set up.
Minerals for Healthy growth
Plants need 4 minerals which are:
Transport in Plants
Multicellular organisms needed transportation systems in them as they can’t absorb everything through diffusion, also it would be too slow due to surface area to volume ratio.
Plants have two main transport systems:
Root hairs :
They take in water by using the hairs that stick out of the roots, they are covered by a lot of microscopic hairs increasing the surface area. They take the water out using osmosis, and they also take minerals out using active transport.
Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.
Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plant’s chance of survival if the transpiration rate can be slowed down. Plants can do this themselves by wilting, or it can be done artificially, like removing some of the leaves from cuttings before they have chance to grow new roots.
Factors that affect transpiration rate
A photometer can be used to measure the transpiration rate.
- Cut the shoot slanted so there is maximum surface area
- Assemble the photometer in water and insert underwater so no water can enter
- Check if apparatus is air tight
- Dry the leaves and allow time for accilamtise and then shut the tap. Remove the end of the capillary rube, until one bubble is formed
- Record the starting position of the bubble
- Start the stop watch and record the distance moved by the bubble per time unit
- Keep the conditions constant throughout the experiment e.g. temperature and air humidity.