Plants can make their own food using Photosynthesis
- Photosynthesis is the process that produces 'food' in plants. The 'food' it produces is glucose
- Photoynthesis happens in the leaves of all green plants
- Photosynthesis happens inside the Chloroplasts (found in leaf cells and other grreen parts of a plant)
- Chloroplasts contain a pigment called chlorophyll which absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. Oxygen is also produced
Carbon dioxide + Water ----> Glucose + Oxygen
Structure of leaf for photosynthesis
How leaves are adapted to for efficient photosynthesis:
- Leaves are broad- large surface area exposed to light
- Most chloroplasts are found in the pallisade layer which is near the top, allowing more light to reach them
- The upper epidermis is transparent (see through) so light can pass through it to the pallisade layer
- Leaves have a network of vasular bundles which are transport vessels (xylem and phloem)-these help support the leaf
- The waxy cuticle helps reduce water loss by evaporation
Rate of photosynthesis
There are 3 factors that limit the rate of photosynthesis
1. Light intensity- Chlorophyll uses light energy to perform photosynthesis. If the light intensity is increased, the rate of photosynthesis will increase steadily, only up to a certain point.
2. Amount of Carbon dioxide- Carbon dioxide is one of the raw materials needed for photosynthesis. Increasing the carbon dioxide will only increase the rate of photosynthesis up to a certain point.
3. Temperature- Temperature effects the enzymes involved. As the temperature increases so does the rate of photosynthesis up to a certain point. If the temperature is too high (over 40C) the plants enzymes will be denatured so the rate of photosynthesis rapidly decreases.
Testing a leaf for starch
1. The leaf is killed by dunking it into boiling water (hold it with tweezers or forceps)-this stops any chemical reactions happening inside the leaf.
2. Next put the leaf in a boiling tube with some ethanol and heat the tube in a water bath-this will get rid of any chlorophyll that's inside the leaf (leaf should end up pale, white-ish colour)
3. Finally rinse leaf in cold water and add a few drops of iodine solution to it. If starch is present it will turn blue-black.
Minerals for Healthy Growth
Plants need three main mineral ions for growth
Plants need certain elements so they can produce important compounds. They get these elements from mineral ions in the soil. If there aren't enough mineral ions in the soil, plants suffer from deficiency symptoms.
- Nitrates-contain nitrogen for making amino acids and proteins. These are needed for cell growth. If a plant can't get enough nitrates it will be stunted and will have yellow older leaves
- Phosphates-contain phosphorus for making DNA and cell membranes and they're needed for respiration and growth. Plants without enough phosphate have poor root growth and purple older leaves.
- Potassium-to help enzymes needed for photosynthesis and respiration. If there is not enough potassium in the soil plants have poor flower and fruit growth and discoloured leaves
- Magnesium is also needed in small amounts as it is required for making chlorophyll. Plants with no magnesium have yellow leaves.
Transport in Plants
VASCULAR BUNDLES located in the roots, stem and leaves of the plants are the transport system.
- The vascular bundles are made up of two main tissue- the XYLEM and the PHLOEM
- These two tissue are seperated by the CAMBIUM
- Transport water and mineral ions
- Carry water and minerals from root to shoot
- Lignified cell walls
- No cytoplasm, nucleus, organelles (non-living)
- Hollow tube (no ends to cells)
Phloem - Sieve tubes
- Transport sucrose (sugars) and amino acids (bi-directional)
- Transport in the phloem=Translocation
- No nucleus, little cytoplasm, sieve plates with pores at 'ends'
- Transpiration is the loss of water from the plant
- Most transpiration happens at the leaves
- Transpiration is caused by the evaporation and diffusion of water from a plants surface
- The evaporation creates a slight shortage of water in the leaf so more water is drawn up from the rest of the plant through the XYLEM VESSELS
- This means more water is drawn up from the roots and so there is a constant transpiration stream of water through the plant
Plants have stomata to allow gas exchange, because there is more water inside the plant than air outside, the water escapes from the leaves through the stomata via diffusion
Factors affecting Transpiration
Transporation Rate is affected by 4 main things:
1. Light Intensity-the brighter the light, the greater the transpiration rate. As it gets darker the stomata begin to close. Photosynthesis can't happen in the dark. When the stomata are closed, very little water can escape.
2. Temperature-the warmer it is, the faster transpiration happens. When it's warm, particles have more energy to evaporate and diffuse out of the stomata.
3. Wind Speed-the higher the wind speed around a leaf, the greater the transpiration rate. If wind speed around the leaf is low, the water vapour just surrounds the leaf and doesn't move away. This means there is a higher concentration of water particles outside the leaf as well as inside so diffusion doesn't happen as quickly.
4. Humidity-the drier the air around the leaf, the faster transpiration happens. If the air is humid, there is a lot of water in the air already so there is not much of a difference between the inside and outside of the leaf.
Diffusion happens fastest if there's a really high concentration in one place and a really low concentration in the other