B8 - Photosynthesis (Y10 - Summer 1) Flashcards
(42 cards)
🟠 What Happens In Photosynthesis?
During photosynthesis, energy is transferred from the environment to the chloroplasts (which contain chlorophyll) by light. This energy is then transferred to convert carbon dioxide from the air, plus water from the soil into a simple sugar called glucose (C6H12O6). The chemical reaction also produces oxygen gas as a by-product. This oxygen is then released back into the air.
🟠 Balanced Chemical Equation For Photosynthesis
. Light .
6CO2 + 6H2O —-> C6H12O6 + 6O2
🟠 What Is Photosynthesis?
Photosynthesis is an endothermic reaction - it needs an input of energy from the environment. The energy transferred from the environment when the bonds holding carbon dioxide and water are borken is more than that transferred back to the environment with the formation of new bonds in glucose and oxygen. The extra energy required for the reaction to take place is transferred from the environment by light.
Some of the glucose produced during photpsynthesis is used immidiately by the cells of the plant for respiration. However, a lot of the glucose is converted into insoluble starch and stored.
🟠 How To Test That A Plant Is Photosynthesising
You can show that a plant is photosynthesising by the oxygen gas it gives off as a by-product. Oxygen is a colourless gas, so in land plants it isn’t easy to show that it’s being produced. However, water plants like Cabomba or Elodea give off visible bubbles of oxygen underwater that you can collect when they photosynthesise. This gas will relight a glowing splint, showing that it is rich in oxygen.
🟠 How Are Leaves Adapted To Photosynthesise Better
Leaves are perfectly adapted organ of photosyntheisis because:
- Most leaves are broad, giving them a big surface area for light to fall on
- Most leaves are thin so diffusion distances for the gases are short
- They contain chlorophyll in the chloroplasts to absorb light
- They have veins, which bring plenty of water in the xylem to the cells of the leaves and remove the products of photosynthesis in the phloem
- They have air spaces that allow carbon dioxide to get to the cells, and oxygen to leave by diffusion
- They have guard cells that open and close the stomata to regulate gas exchange
🟠 Example Of An Organisms Adapted To Photosynthesising In Water
Algae are aquatic, so they are adapted to photosynthesising in water. They have a large surface area and absorb carbon dioxide dissolved in the water around the,. The oxygen they produce also dissolves in the water around them as it is released.
🟠 How Is Light A Limiting Factor For Photosynthesis?
The most obvious factor affecting the rate of photosynthesis is light intensity. If there is plenty of light, lots of photosynthesis can take place. If there is very little or no light, photosynthesis will stop, whatever the other conditions around the plant are. For most plants, the brighter the light, the faster the rate of photosynthesis.
🟠 How Is Temperature A Limiting Factor For Photosynthesis?
Temperature affects all chemical reactions, including photosynthesis. As the temperature rises, the rate of photosynthesis increases as the reaction speeds up. However, photosynthesis is controlled by enzymes. Most enzymes are denatured once the temperature rises around 40°C - 50°C. If the temperature gets too high, the enzymes controlling photosynthesis are denatured and tbe rate of photosynthesis will fall as a result.
🟠 How Carbon Dioxide Concentration Can Be A Limiting Factor For Photosynthesis
Plants need carbon dioxide to make glucose. The atmosphere is only about 0.04% carbon dioxide. This means carbon dioxide often limits the rate of photosynthesis. Increasing the acrbon dioxide concentration will increase the rate of photosynthesis.
On a sunny day, carbon dioxide concentration is the most
common limiting factor for plants. The carbon dioxide
concentrations around a plant tend to rise at night, because
in the dark a plant respires but doesn’t photosynthesise.
As light intensity and temperature increase in the
morning, most of the carbon dioxide around the plant
gets used up.
🟠 How do Chloroplasts help with Photosynthesis
These are found in the green parts of a plant. They are green because they contain a substance called chlorophyll, which abosorbs light so the plant can make food photosynthesis. Each chloroplast is around 3-5µm long. (Root cells do not have chloroplasts because they do not photosynthesise.
🟠 How do Guard Cells help with Photosynthesis
These open and close the stomata based on when products for pohotosynthesis are needed, but in relation to how much water the plant will lose in doing this.
🟠 How do Stomata help with Photosynthesis
The stomata control gas exchange in the leaf. Each stoma can be open or closed, depending on how turgid its guard cells are. In the light, the guard cells absorb water by osmosis, become turgid and the stoma opens. In the dark, the guard cells lose water, become flaccid and the stoma closes.
🟠 How do Air Spaces help with Photosynthesis
Air spaces with high surface areas allow gases to diffuse far easier and far more effectively, making the process of photosynthesis more effective and rapid.
🟠 How Can Humans Control CO2, Light, And Temperature Levels And Affect Plant Photosynthesis
In a science lab or a greenhouse the levels of carbin dioxide can be increased artificially. This means that carbon dioxide is no longer the limiting factor or a sunny day for example. Then the rate of photosynthesis increases with the rise in carbon dioxide concentration.
In a garden, woodland or field (rather than a lab or greenhouse, where the conditions can be controlled), light intensity, temperature, and carbon dioxide concentrations interact, and any one of them might be the limiting factor of photosynthesis at any given moment.
🟠 How Is Chlorophyll A Limiting Factor For Photosynthesis
If the amount of chlorophyll in a lead is limited in any way, less photosynthesis will take place. The leaves of some ornamental plants have white, chlorophyll-free areas. The plants grow less vigorously than plants witn all green leaves. If they are permanently in dim light, variegated leaves often turn completely green. If a plant does not habe enough minersls, especially magnesium, it cannot make chlorophyll. The rate of photosynthesis drops and eventually the plant
🟠 What Is Light Intensity And The Inverse Square Law
The relationship between light intensity and the rate of photosynthesis is not a simple one. This is because light intensity involves the inverse square law.
As the distance of the light from the plant increases, the light intensity decreases (Light intensity decreases in proportion to the square of the distance - the inverse square law). That is an inverse relationship - as one goes up the other goes down. However, the relationship between distance and light intensity is not linear. The light intensity decreases or increases in inverse proportion of the square of the distance
Light Intensity ∝ 1 / Distance^2
For example, if you double the distance between the light and your plant, light intensity falls by a quarter.
Light Intensity ∝ 1/2^2 = 1/4
🟠 What is Photosynthesis?
Photosynthesis is when light energy is harnessed by the plant. The light energy is used to convert carbon dioxide and water into glucose. This essentially coverts light energy into chemical energy in the form of glucose. Oxygen is released as a by-product.
🟠 How Do Plants Use Glucose
Plant cells and algal cells, like any other living cells, respire all the time. They use some of the glucose produced during photosynthesis as they respire. The glucose is broken down using oxygen to provide energy for the cells. Carbon dioxide and water are the waste products of the reaction. Chemically, respiration is the reverse of photosynthesis.
🟠 How Does The Plant Use Glucose To Strengthen Cell Walls?
Energy transferred in respiration may be used to build smaller molecules into bigger molecules. For example, plants build up glucose into complex carbohydrates such as cellulose. They use this to strengthen their cell walls.
🟠 How And Why Does The Plant Turn Glucose To Starch And What Does It Do With It?
Plants convert some of the glucose produced in photosynthesis into starch to be stored. Glucose is soluble in water. If it were stored in plant cells, it could affect the way water moves into and out of the cells by osmosis. Lots of glucose stored in plant cells could affect the water balance of the whole plant.
Starch is insoluble in water. It has no effect on the water balance of the plant so plants can store large amounts of starch in their cells. Starch is the main energy store in plants and it is found in cells all over a plant:
- Starch is stored in the cells of the leaves. It provides an energy store for when it id dark of when light levels are low.
- Starch is also kept in special storage areas of a plant. For example, many plants produce tubers and bulbs that are full of stored starch, to help them survive through the winter. Humans often take advantage of these starch stores, found as vegetables such as potatoes and onions.
🟠 How Do Plants Use Glucose To Make Proteins?
Plants use some of the glucose from photosynthesis to make amino acids. They do this by combining sugars with nitrate ions and other mineral ions from the soil. These amino acids are then built up into proteins to be used in the plant cells in many ways, including as enzymes. This uses energy from respiration.
Alage also make amino acids. They do this by taking the nitrate ions and other materials they need from the water they live in.
🟠 How Do Some Plants Survive With Low Levels Of Minerals And Nutrients?
Very few plants can survive well in the soil you are growing in is low in minerals. For example, bogs are wet and their peaty soil has very few nutrients in it. This makes it a difficult plce for plants to live in.
Some carnivorous plants, such as pitcher plants, Venus flytraps, and sundews are especially adaoted to live in nitrate-poor soil. They can survive because they obtain most of their nutrients from the animals, such as insects they trap. They then use nutrates and other minerals from the digested bodies of their victims in place of the nutrients they cannot get from the bog soil in which they grow. After an insec has been digested, the trap reopens, ready to try again.
🟠 How Plants Use Glucose To Make Lipids?
Plants and algae use some of the glucose from the photosynthesis and energy transferred fromrespiration to build up fats and oils. These may be used in the cells as an energy store. They are sometimes used in the cell walls to make them stronger. In addition, plants often use fats or oils as an energy store in their seeds. Seeds provide food for the new plant to respire as it germinates. Some algal cells are also very rich in oils.
🟠 Two Important Points To Remember About How Often Plants Respire And Whether Glucose And Starch Are Soluble In Water?
- Plants respire 24 hours a day to transfer useable energy for the cells
- Glucose is soluble in water, but starch is insoluble.
