Chapter 6: Photosynthesis Flashcards
Define photosynthesis [2]
The process through which plants convert carbon dioxide and water with the help of sunlight and chlorophyll into glucose and the by-product oxygen.
Describe the word equation for photosynthesis [1]
carbon dioxide + water –> glucose + oxygen in the presence of light and chlorophyll
Describe the chemical equation for photosynthesis [1]
6 CO2 + 6 H2O —> C6H12O6 + 6 O2 in the presence of sunlight and chlorophyll
Describe the function chloroplast [4]
- Absorbs light energy through the green pigment named chlorophyll stored inside it
- Transfers light energy to chemical energy
- Energy is used to combine CO2 and H2O with the help of enzymes to make glucose (site of photosynthesis)
- Synthesizes carbohydrates
Describe the structure of chloroplast [4]
- Contains thylakoids which are disc-like sacs found in the inner membrane of the chloroplast
- It has a double membrane
- On the thylakoids chlorophyll is found
- A stack of thylakoids is known as a grana
Explain the uses and storage of carbohydrates in different forms in a plant [5+5]
(a) starch as an energy store - glucose is turned into starch and can be used later. They are turned into starch because glucose is soluble in water and may get involved in chemical reactions taking pace in cells. Starch does not affect the concentration of solutions inside the cell so they do not cause water to leave or enter via osmosis.
(b) cellulose to build cell walls - cellulose is made by linking glucose molecules in long chains
(c) glucose used in respiration to provide energy - eg: energy is used in transporting mineral ions into the root hairs by active transport. It is also required to build protein molecules from amino acids for growth.
(d) sucrose for transport in the phloem - Some parts of the plant require glucose to be delivered to them. Therefore the glucose is converted into sucrose for easier transport, as it contains more energy than a monosaccharide.
(e) nectar to attract insects for pollination - attracts insects to pollinate pollen grains from one flower to another
Which 2 mineral ions do plants require? [2]
- Magnesium
- Nitrogen
Why do plants require the 2 ions? What would happen without them? [4]
- Nitrate ions: to make amino acids and then proteins. Without them the plant will have weak growth and yellow leaves
- Magnesium ions: to make chlorophyll. Without them the leaves will turn yellow, often between the veins
External features of the leaf and how they make the leaf adapted for photosynthesis [4]
- Large surface area - allows for large amounts of sunlight to fall on the leaf and allows for more carbon dioxide to diffuse into the leaf from air
- Thin - allows sunlight to pass through the leaf, allowing the cells inside to photosynthesis. Allows carbon dioxide to reach all the cells quickly through diffusion.
List all the internal parts of a leaf [10]
chloroplasts, cuticle, guard cells and stomata,
upper and lower epidermis, palisade mesophyll,
spongy mesophyll, air spaces, vascular bundles,
xylem and phloem
State how each part of the internal features of a plant is adapted to photosynthesis. State the function of each part. [10]
- Cuticle - a transparent waxy layer
which is found on the outermost surface of leaves. It prevents the loss of water due to transpiration - Epidermis - transparent layer with no chlorophyll, closely packed cells, stomata found in the lower epidermis. Allows sunlight to penetrate into the mesophyll layer, protects the leaf and prevents the entry of microbes, allows diffusion of CO2 into and O2 out of the leaf
- Mesophyll layers - contains cells with lots of chloroplasts. Chlorophyll in chloroplast absorbs light energy for photosynthesis in palisade and spongy mesophyll cells
- Palisade mesophyll tissue - contains numerous chloroplasts so chlorophyll in chloroplasts can absorb light energy. Cells are elongated and arranged lengthways and end on so less cell walls scatter light. Palisade cells are closely packed together allowing for maximum absorption of sunlight.
- Spongy mesophyll tissue - oval cells with air spaces between them, allowing for diffusion of CO2 into the mesophyll cells and helping in floating/buoyancy
- Xylem and phloem - found in the midrib
and veins of the leaf, form the vascular bundles, close to the mesophyll tissues. Xylem helps in transport of water and minerals to the leaf for photosynthesis. Phloem transports products of photosynthesis (sugars) from leaves to other plant organs.
Design an experiment to test the presence of starch in a leaf [4]
Take a variegated leaf and place it in a beaker filled with boiling water for 20 seconds, to denature the enzymes and stop photosynthesis. Take the leaf out. Boil ethanol by placing a test tube in the water bath. Put the leaf in ethanol for around 2 minutes or until all the chlorophyll is removed. Take the leaf out and run it under water for a few seconds till it is soft. Place it on a while tile. Pour a few drops of iodine solution all over the leaf. Wherever starch is present it will turn from orange to blue-black.
Design an experiment to test the necessity of chlorophyll for photosynthesis
Take a plant with variegated leaves. Place the potted plant in complete darkness for 2-3 days to destarch it (to remove any starch that was produced in the leaves prior to the experiment). Place it in sunlight for several hours after. Pluck a leaf and place it in a test tube with water and place in a water bath to boil. Take out after 2 minutes and place the leaf it in an ethanol solution and place it in a water bath. Boil till all the color leaves the leaf. Rinse the leaf under water to soften it. Use a dropper to put iodine solution all over the leaf after placing it on a white tile. Wherever starch is present, iodine will turn from brown to blue-black. All the green parts of the leaf would’ve turned blue black.
Safety precaution: do not boil ethanol over an open flame
Design an experiment to test the necessity of light for photosynthesis
Destarch the plant for 2-3 days. Take it out of the dark and cut a piece of black paper and secure the cut end of the paper using a sticky tape.
Cover both surfaces of one of the leaves using this piece of black paper, and secure the paper on the leaf using some paper clips. Leave the potted plant in sunlight for several hours. Then, detach the leaf from the plant and remove the black paper from the leaf. Now, introduce the leaf into the test tube containing the alcohol solution. Place the tube in the boiling water bath until the leaf loses its color. Remove the leaf from the ethanol. Briefly place the leaf for a few seconds in the hot water bath in order to soften the leaf. Transfer the leaf onto a white tile and use a dropper to spread iodine solution on the entire leaf.
Safety precaution: do not boil ethanol over an open flame
Design an experiment to test the necessity of CO2 for photosynthesis
Place 2 potted plants with normal green leaves in a dark place for 48 hours to destarch. Test one of the leaves from each plant to ensure they are fully destarched. Place both in a bell jar. On the funnel on top of the bell jar, there is soda lime and inside the bell jar, there is sodium hydroxide in the beaker. Both of these absorb all the CO2 and ensure none of it enters the bell jar. In the other bell jar there is chalk on the funnel and the beaker has water to ensure there is CO2. Place both bell jars in sunlight for 48 hours. Use iodine solution to test the presence of starch. The one with CO2 available will have starch as seen by the iodine solution turning from brown to blue black. The one without CO2 won’t have starch.
