Photosynthesis
Photosynthesis means “making with light”. It is the process by which plants make useful glucose out of the raw materials water and carbon dioxide, using light energy from the sun.
Water is essential for photosynthesis, it is sucked up from the soil by the roots and transported up the stem to leaves where it is put into use. Carbon dioxide, just like water is essential for photosynthesis. It moves into the leaf from the air by diffusion, through the stomata (tiny wholes in the leaf). Once carbon dioxide and water are present in the leaf, one condition for photosynthesis is needed, that is light. The two cells in the diagrams are called palisade cells (the rectangular one) and spongy mesophyll cell (the circular one), these are the cells where photosynthesis take place. They a structure called chloroplasts, these structures contain a green pigment named chlorophyll, this is to trap sunlight to be used in energy, a large number of chloroplasts is required for photosynthesis. |
How photosynthesis happen:
Word equation for the Photosynthesis
- Carbon dioxide and water enter the cell
- The cell traps light energy using chloroplasts
- The energy is used to split water (H2O) into hydrogen and oxygen
- The oxygen is excreted outside the leaf to the atmosphere as a waste product
- The hydrogen reacts with carbon dioxide forming glucose.
Word equation for the Photosynthesis
Factors Affecting The Rate Of Photosynthesis:
- Availability of light
- The presence of green pigment to absorb the light
- a supply of Carbon dioxide and water
- a temperature suitable for enzyme activity
Chlorophyll
Plant must have chlorophyll in order to photosynthesis, as this is the substance which converts light energy into chemical energy.
Chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage.
Plants also need carbon dioxide and water, to convert into oxygen and glucose. All these should be plentiful, otherwise the plant’s photosynthesis will slow down.
Plants take in carbon dioxide from air through their stomata (on the leaves) using diffusion and they absorb water through their root hair cells using osmosis.
Define the term limiting factor
Define the term limiting factor as something present in the environment in such short supply that it restricts life processes. The three possible limiting factors of photosynthesis are carbon dioxide, temperature, and light intensity. When the carbon dioxide concentration is too low, the rate of reaction is low. The same happens with temperature and light intensity.
Plants at night: At night, the plant performs several process to convert the stored starch into many useful nutrients like:
- Sugars for respiration
- Cellulose and proteins for making cells and cell walls
- Vitamins to help in energy action
- Fats as a long term storage material
- Remaining starch is temporarily stored.
The importance of:
Nitrate ions: for protein synthesis (making proteins)
Magnesium ions: for chlorophyll synthesis (making chlorophyll)
The effects of nitrate ion deficiency: The plant has poor growth and yellowed leaves
The effects of magnesium ion deficiency: Plant leaves become yellow
The uses of nitrogen fertilizers
Since nitrogen fertilizers provide nitrogen ions, it allows plants to form more proteins, and therefore promotes the growth of plants and fruits.
The dangers of overuse of nitrogen fertilizers
Excess nitrogen can be dangerous to agriculture. Water may pass from the plants to the soil resulting in the wilting of the plant. In case of heavy rainfall, the fertilizer may be washed away in rivers and which may result in the rapid growth of water plants, thus decreasing the amount of oxygen in the water and causing an increase in the amount of bacteria as the plant and other creatures die. In short it also causes water pollution.
Light and Dark reaction in Photosynthesis
Light Reaction (involves the sun)
The roots suck up water from the ground, into the chloroplasts. In there, the water is sun-heated and gets split into hydrogen, oxygen and ATP. The oxygen then gets released for us to breath and the hydrogen is put to a different part of the leaf. Dark Reaction (doesn't involve the sun) After the hydrogen gets to the other part of the leaf, the CO2 (carbon dioxide), that we breath out, mixes with the hydrogen and gets fused using ATP, making sugar/starch. |