B8 - Photosynthesis (Y10 - Summer 1)

Question 1

🟠 What Happens In Photosynthesis?

Answer 1

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.

Question 2

🟠 Balanced Chemical Equation For Photosynthesis

Answer 2

. Light .

6CO2 + 6H2O —-> C6H12O6 + 6O2

Question 3

🟠 What Is Photosynthesis?

Answer 3

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.

Question 4

🟠 How To Test That A Plant Is Photosynthesising

Answer 4

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.

Question 5

🟠 How Are Leaves Adapted To Photosynthesise Better

Answer 5

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

Question 6

🟠 Example Of An Organisms Adapted To Photosynthesising In Water

Answer 6

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.

Question 7

🟠 How Is Light A Limiting Factor For Photosynthesis?

Answer 7

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.

Question 8

🟠 How Is Temperature A Limiting Factor For Photosynthesis?

Answer 8

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.

Question 9

🟠 How Carbon Dioxide Concentration Can Be A Limiting Factor For Photosynthesis

Answer 9

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.

Question 10

🟠 How do Chloroplasts help with Photosynthesis

Answer 10

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.

Question 11

🟠 How do Guard Cells help with Photosynthesis

Answer 11

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.

Question 12

🟠 How do Stomata help with Photosynthesis

Answer 12

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.

Question 13

🟠 How do Air Spaces help with Photosynthesis

Answer 13

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.

Question 14

🟠 How Can Humans Control CO2, Light, And Temperature Levels And Affect Plant Photosynthesis

Answer 14

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.

Question 15

🟠 How Is Chlorophyll A Limiting Factor For Photosynthesis

Answer 15

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

Question 16

🟠 What Is Light Intensity And The Inverse Square Law

Answer 16

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

Question 17

🟠 What is Photosynthesis?

Answer 17

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.

Question 18

🟠 How Do Plants Use Glucose

Answer 18

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.

Question 19

🟠 How Does The Plant Use Glucose To Strengthen Cell Walls?

Answer 19

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.

Question 20

🟠 How And Why Does The Plant Turn Glucose To Starch And What Does It Do With It?

Answer 20

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.

Question 21

🟠 How Do Plants Use Glucose To Make Proteins?

Answer 21

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.

Question 22

🟠 How Do Some Plants Survive With Low Levels Of Minerals And Nutrients?

Answer 22

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.

Question 23

🟠 How Plants Use Glucose To Make Lipids?

Answer 23

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.

Question 24

🟠 Two Important Points To Remember About How Often Plants Respire And Whether Glucose And Starch Are Soluble In Water?

Answer 24

• Plants respire 24 hours a day to transfer useable energy for the cells
• Glucose is soluble in water, but starch is insoluble.

Question 25

🟠 How Can You Test If A Plant Is Photosynthesising?

Answer 25

You can see if a plant has been photosynthesising if it returns a postive test for starch (because starch is what plants store glucose as). To find out whether this starch is from photosynthesising and not just already on the surface, you can block light from shining on part of a leaf by covering it with tape. The part that has been taped should return a negative test for starch and the part that hasn’t been taped should be positive. This shows the starch produced from the leaf has come from photosynthesis.

Question 26

🟠 Method on How To Test For Starch On A Leaf

Answer 26

Iodine solution is used to test leaves for the presence of starch. You need to:

1. Heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
2. Add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
3. Wash with water to rehydrate and soften the leaf and spread onto a white tile
4. Add iodine solution from a dropping pipette

After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.

Question 27

🟠 What Happens To A Fully De-Starched Leaf When You Test It For Starch

Answer 27

A fully de-starched leaf does not test positive for starch at all, meaning it will be the same colour all over. This is because leaf has used up all of it’s starch store while being without any light to stay alive. This is why it doesn’t turn blue black.

Question 28

🟠 What Happens To A Partly De-Starched Leaf When You Test It For Starch

Answer 28

A partly de-starched leaf only partly tests positive for starch, meaning part of it will be blue/black (showing a positive test for starch), and the de-starched part of the leaf will not be as blue/black, showing it doesn’t have as much starch, or no starch at all.

Question 29

🟠 What Happens To A Variegated Leaf When You Test It For Starch

Answer 29

The Variegated Leaf on the right shows a positive test for starch in the areas which contained chlorophyll, and a negative test for starch in the areas which lack chlorophyll.

This is evidence that chlorophyll is required for photosynthesis.

Question 30

🟠 What Is A Limiting Factor? (+ The 3 / 4 limiting factors of photosynthesis)

Answer 30

A limiting factor a variable of a system that causes a noticeable change in output or another measure of a type of system, so essentially, a limiting factor limits the ‘amount’/rate of photosynthesis that can take place in a plant for example. Some limiting factors of Photosynthesis are: Light Intensity, Temperature and Carbon Dioxide (+ Chlorophyll in Chloroplasts).

Question 31

🟠 How Is The Garden Greenhouse Useful

Answer 31

Farmers use huge plastic ‘polytunnels’ as giant greenhouses for growing crops from to atoes to strawberries and potatoes. Greenhouses are able to affect the rate kf phptosynthesis for different plants. This glass/plastic building means that the environment is much more controlable than an ordinary garden or field. Most importantly, the atomosphere is warmer inside than out. This affects the rate of photosynthesis, speeding it up so plants grow fasters, flower, and fruit earlier, and crop better.

This means greenhouses can be used to grow fruits that wouldn’t usually be able to grow as well when outside, like peaches and lemons in the UK.

Question 32

🟠 What Are Limiting Factors in Garden Greenhouses?

Answer 32

In the laboratory you can isolate different factors and see how they limit the rate of photosynthesis. However, for most plants it is usually a mixture of these factors that affects them. Early in ther morning, light levels and temperature probably limit the rate of photosynthesis. Then as the levels of light and temperature rise, carbon dioxide levels become limiting. On a bright, cold winter day, temperature probably limits the rate of the process. There is a constant interaction between the different factors.

Question 33

🟠 What Do Big Greenhouses Control (+ What Are Hydroponics)

Answer 33

Big commerical greenhouses now take advantage of limiting factors. They control not only the temperature, but also the levels of light and carbon dioxide to get the fastest possible rates of photosynthesis. As a result the plants grow as quickly as possible. The plants are even grown in water with a perfect balance of nutrients instead of soil to make sure nothing slows their growth. This type of system is known as hydroponics.

Question 34

🟠 The Benefits Of Using Greenhouses

Answer 34

These greenhouses are enormous and conditions are controlled using computer software. It costs a lot of money but manipulating the environment has many benefits. You can change the carbon dioxide levels in the greenhouses during the day as well as the temperature amd the light levels. Furthermore, you can change the mineral content of the water as the plants get bigger.

Turnover is fast which means profits can be high. The crops are clean and soil-free. There is no need to plough or prepare the land un these systems, and crops can be grown where the land is poor.

Question 35

🟠 What Are Done To Greenhouses To Try And Prevent Losses (and get Profits)

Answer 35

Electricity and gas are used to maintain the lighting and temperatures and to control the carbon dioxide levels. Expensive monitoring equipment and computers are needed to maintain conditions inside the greenhouse within narrow boundaries, and alarms are vital if things go wrong.

On the other hand, less staff are needed, the time from seed to harvest, along with the size of the businness have to be considered when deciding whether an enclosed system will increase or reduce profits. The increased income from a larger crop and the ability to grow more crops each year has to be balanced against the cost of setting up and maintaining the system.

To eliminate limiting factors, plants can be grown hypotonically.

Question 36

🟠 What Crops would be good to grow Hypotonically?

Answer 36

I think crops like rice and potatoes (along with tomatoes, peas, and cucumbers) would be good to grow hypotonically because they will have the greatest affect on these two crops for example, and will therefore give the biggest percentage yield, making them gold options. The higher yield along with the fact for the high demand of these two peodycts mean that growing these would be a good economical option.

Question 37

🟠 What Crops would not be good to grow Hypotonically?

Answer 37

I think crops like wheat and cabbages would be bad to grow in this way, as they will not recieve as much benefit in terms of their percentage yield compared to the other better options, mean g it might not be worth it if your actually trying to sell these products.

Question 38

🟠 Why Do Oil Palms Grow Rapidly In Rainforest Conditions And What Is The Glucose Made From Oil Palms Used For In The Plant?

Answer 38

Oil palms can grow rapidly in rainforest conditions because there is a good supply of heat, along with an abundance of sunlight. These are factors of photosynthesis, so with lots of heat and sun, the oil palms will be able to grow very quickly, while one of their few limiting factors may Carbon Dioxide at some points.

Question 39

🟠 What Does The Oil Palm Plant use it’s Oil for (+ What actually is the oil)

Answer 39

The oil in the palm fruit is from the glucose made in photosynthesis, and the oil is used as an energy store in the plant, allowing it grow, as the seed can germinate and grow, but can already have the products to photosynthesise.

In the plant, glucose is used in the plant’s respiration, meaning it can release the energy it needs to function, grow, and live. Glucose will also be used for building complex substances like cellulose and starch for example. Finally, energy is used in Active Transport and combines with nitrates to make amino acids and proteins.

Question 40

🟢 Isotonic Definition

Answer 40

If the concentration of solutes in the solution outside the cell is the same as the internal concentration, the solution is isotonic to the cell

Question 41

🟢 Hypertonic Definition

Answer 41

If the concentration of solutes in the solution outside the cell is higher than the internal concentration, the solution is hypertonic to the cell

Question 42

🟢 Hypotonic Definition

Answer 42

If the concentration of solutes outside the cell is lower than the internal concentration, the solution is hypotonic to the cell