B5 : Photosynthesis Flashcards
Uses of glucose
- The glucose produced by photosynthesis is mainly used for respiration in plants.
- However, it can also be converted into other products such as protein, fats and oils, cellulose, and starch
Uses of protein
- Proteins are needed for cell growth and repair.
- A source of nitrogen is also needed for glucose to be converted into proteins.
- Plants get this nitrogen by absorbing nitrate ions (minerals) from soil.
Uses of fats and oil
- Fats and oils are stored in structures such as seeds.
2. For example, sunflower seeds are a key ingredient in cooking oils.
Uses of cellulose
Cellulose is used to strengthen cell walls. It is particularly important for fast-growing plants.
Uses of starch
Starch is insoluble (cannot be dissolved) and is stored in stems, leaves or roots.
Ion Deficiencies
- Plants need many mineral ions (minerals) for healthy growth.
- They extract most of these mineral ions from the soil. If the soil quality is poor, plants can suffer from ion deficiency conditions (disorders).
- Ion deficiencies include Nitrate deficiency and Magnesium deficiency
Nitrate deficiencies
- Nitrates are needed for the production and synthesis (creation) of amino acids/proteins.
- Amino acids are needed for protein synthesis
- Without proteins, plants cannot grow. This means that a nitrate deficiency causes stunted growth.
Magnesium deficiency
- Magnesium is required for the production of chlorophyll.
- Magnesium deficiency causes chlorosis: The plant cannot photosynthesise well. This means that it cannot produce the glucose needed for healthy growth.
- When magnesium is absent, plant leaves are yellow.
key factors affecting the rate of photosynthesis
- Temperature
- Carbon dioxide concentration
- Light intensity
- Chlorophyll Concentration
Light Intensity
- Increasing light intensity increases the rate of photosynthesis because more energy is provided.
- However, if the light intensity is increased above a certain threshold, the rate of photosynthesis can no longer be further increased by lights intensity because another factor (such as temperature) is limiting the rate of the reaction.
Chlorophyll Concentration
High chlorophyll concentration gives a high rate of photosynthesis.
Carbon Dioxide Concentration
- Increasing the carbon dioxide concentration increases the rate of photosynthesis.
- However, above a certain threshold, the rate of photosynthesis cannot be further increased by carbon dioxide concentration because another factor (such as light intensity) is limiting the rate of reaction.
Temperature
- Increasing the temperature increases the rate of photosynthesis because more energy is provided.
- However, if the temperature is increased to above about 45°C, the enzymes that catalyse (speed-up) the reaction begin to denature (not work anymore).
- This causes the rate of the reaction to drop sharply until it stops altogether.
Photosynthesis Word Equation
Carbon Dioxide + water (arrow) Glucose + Oxygen
Photosynthesis Chemical Equation
6CO2 + 6H20 → C6H12O6 + 6O2
Limiting Factors
- A limiting factor is a factor or resource that’s in such short supply, the rate of photosynthesis is limited by it.
- The identity of the limiting factor in photosynthesis depends on the conditions faced by the plant
- Situations where limiting factors may occur include winter, night, warm and bright, and mineral-deficient soil
Winter
In winter, temperature is usually the limiting factor.
Night
At night, light intensity is usually the limiting factor.
Warm and Bright
In warm and bright conditions, carbon dioxide concentration is usually the limiting factor.
Mineral-deficient Soil
- If plants are grown in mineral-deficient (lacking minerals) soil, they may not absorb enough minerals to produce lots of chlorophyll.
- In this case, chlorophyll concentration can be the limiting factor.
Testing the rate of photosynthesis
- You can easily investigate the effect of light intensity on the rate of photosynthesis by using an aquatic (lives in water) plant like pondweed.
- To do this, change the distance between the lamp and the pondweed and count the number of bubbles (oxygen) produced.
- In this experiment, light intensity is the independent variable (and limiting factor) and the number of bubbles is the dependent variable.
Photosynthesis
- Photosynthesis is the process by which plants make carbohydrates from raw materials, using energy from light.
- Green plants make the carbohydrate glucose from carbon dioxide and water. At the same time oxygen is produced. Plants need energy of sunlight for this. This reaction is called photosynthesis
Process of photosynthesis
- light energy is absorbed by chlorophyll - a green substance found in chloroplasts in green plant cells and algae
- absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
- oxygen is released as a by-product
Variegated leaves
Some leaves have white patches where there is no chlorophyll. These are called variegated leaves.
Testing a leaf for starch
- Boil the leaf to kill it and stop photosynthesis.
- Place it into alcohol and boil to remove chlorophyll.
- Place into water to soften the leaf and remove excess alcohol.
- Place onto a petri dish and add iodine.
- If the iodine changes from orange/brown to blue/black starch is present.
Chlorophyll
- This is where photosynthesis occurs.
- Chloroplasts contain chlorophyll which allows light energy to be absorbed and converted to chemical energy.
- pigment that makes plants look green
- when sunlight falls on chlorophyll molecule, some of the energy in the light is absorbed, and the molecule then releases energy to make carbon dioxide combine with water, with the help of enzymes inside the chloroplasts to convert light energy into chemical energy
