Chapter 10 Photosynthesis

Question 1

State the function of the upper epidermis of a leaf

Answer 1

• Transparent cells (no chloroplasts) which covers the upper surface of the leaf
• Allows light to pass through
• Protect the inner cells
• Produce the cuticle

Question 2

State the function of the cuticle on a leaf

Answer 2

• Waxy, waterproof layer covering the upper epidermis of the leaf
• Reduces water from evaporating from the leaf

Question 3

State the function of the lower epidermis of the leaf

Answer 3

• Transparent, covers the lower surface of the cell

- Allows light to pass through, protects inner cells and sometimes also produces a cuticle

Question 4

Name the different layers of which a leaf consists

Answer 4

• Upper epidermis
• Lower epidermis
• Cuticle
• Mesophyll layer
• Vascular bundles
• Stomata

Question 5

Describe the mesophyll layer?

Answer 5

• it is the middle layer of the leaf situated between the two epidermises.
• the mesophyll layer just below the upper epidermis is called the palisade mesophyll cells.
• the palisade mesophyll is where most photosynthesis takes place.
• The mesophyll layer in the lower part of the leaf just above the lower epidermis layer is called the spongy mesophyll cells.
• spongy mesophyll cells are loosely arranged and rounder with large air spaces between them
• this allows for gaseous exchange by diffusion between the cells.

Question 6

What are vascular bundles or veins?

Answer 6

• The vascular bundles are made upof xylem and phloem.
• Xylem is made up of tiny tubes called xylem vessels which transports inorganic substances.
• Phloem is made up of phloem sieve tubes and companion cells.

Question 7

Describe the stomata and its fuctions.

Answer 7

• Stomata are found in the lower epidermis between the cells.
• These are small pores with two guard cells on either side of the opening.
• they control the opening and closing of a stoma.
• the stomata allow gaseous exchange where carbon dioxide and oxygen can diffuse in or out of the leaf.
• allows transpiration to take place.
• guard cells contain few chloroplasts so some photosynthesis can take place her.

Question 8

Study diagram on page 177

if still uncertain what to do, read below.

Answer 8

hi…. i’m Bob. I’m a goldfish. A gold fish has a memory of…hi….i’m bob.

Question 9

Discuss the ways in which the structure of a leaf has adapted to carry out photosynthesis.

Answer 9

• Very large suface area for maximum amount of light.
• thin to allow light to penetrate.
• thin to reduce distance of diffusion.
• supported by a stem and petiole to expose as much of it as possible.

Question 10

Describe how the upper and lower epidermis layers are adapted to support photosynthesis

Answer 10

• Tranparent to allow light to pass to the mesophyll layer

Question 11

Describe how the palisade mesophyll layer in a leaf is adapted to carry out photosynthesis

Answer 11

• Closely packed cells to absorb more light
• Cells are near the surface of the leaf to maximise light interception
• Cells are arranged at right angles to the leaf surface to reduce the number of cell walls light needs to travel through
• Cells have large numbers of choloroplasts to maximise light absorbtion

Question 12

Describe how the spongy mesophyll layer is adapted to carry out photosynthesis

Answer 12

• Cells are round and loosely arranged to have air spaces, which act as reservoirs for gases and assist in gaseous exchange
• Mesophyll cells in general have large vacuoles to push chloroplasts to the edge of the cell
• Mesophyll cells in general have thin cell walls for a short diffusion pathway

Question 13

Describe how chloroplasts are adapted to carry out photosynthesis

Answer 13

• Can move within the mesophyll to the light

- Can move away from intense light to avoid damage

Question 14

Describe how stomata are adapted to assist in photosynthesis

Answer 14

• Holes in the lower epidermis for gases to enter and leave during gaseous exchange

Question 15

Describe how xylem and phloem assist in the process of photosynthesis

Answer 15

• Xylem is present for the transport of water to chloroplasts in the mesophyll cells
• Phloem for translocation of the products of photosynthesis away from the leaf

Question 16

Name the steps in carrying out starch tests on leaves

Answer 16

Take a green leaf which was exposed to sunlight for a few hours (where glucose was produced and changed into starch for storage)

1. Boil the leaf until flabby (to destroy cell walls, membranes, cytoplasm and enzymes for iodine penetration
2. Place the leaf in a test tube with ethanol and then in a beaker with boiling water until the leaf is decolourised (for chlorophyll to be dissolved and extracted)
3. Rinse the leaf in hot water (to soften it which is hardened by alcohol)
4. Spread the leaf in a shallow petri dish or on a white tile and cover it with yellow-brown iodine solution for a few minutes

If the leaf turns blue-black, starch is present

Question 17

Describe how starch would be removed from a plant

Answer 17

• Place potted plant in dark cupboard for 48 hours
• This will ensure that no starch will be formed in the leaves during that period
• Any starch already present will be converted to glucose to be transported out of the leaves
• When the leaf is now tested no starch will be present
• The plant is now said to be destarched

Question 18

Describe how one would show that light is essential for photosynthesis

Answer 18

• Destarch a potted geranium plant
• Select one leaf at the top of a leafy shoot, but do not remove it
• Wrap a strip of aluminium foil around this leaf and make sure it can not receive any light
• Expose the plant to sunlight for 4-6 hours
• Remove the leaf and the foil and test the leaf for starch
• The exposed parts will turn blue-black
• The covered portion will stain brown
• Starch did therefore not form when light was not received, and light is necessary for starch formation and thus for photosynthesis

Question 19

Describe how one would show that carbon dioxide is necessary for photosynthesis

Answer 19

• Destarch a potted geranium plant
• Put a small container with soda lime or potassium hydroxide or sodium hydroxude close to the plant
• Cover it with a transparent plastic bag tightly sealed with an elastic band so that no carbon dioxide can enter
• The soda lime will absorb all carbon dioxide in the bag
• Expose the plant to sunlight for 4-6 hours
• Remove the leaves and test the leaf for starch
• The leaves stain brown
• Since starch did not form when the plant did not receive carbon dioxide, it seems carbon dioxide is necessary for starch formation and thus photosynthesis

Question 20

Describe how one would show that chlorophyll is essential for photosynthesis

Answer 20

• Destarch a potted geranium plant which has variegated leaves
• Expose the plant to sunlight for 4-6 hours
• Remove the leaf and make a careful drawing of its green and non-green parts
• Test the leaf for starch
• The green parts (chlorophyll) will turn blue black
• The brown parts (no chlorophyll) will stain brown
• Since starch is present only in the green parts, it seems reasonable to assume that chlorophyll is essentail for starch production and thus photosynthesis

Question 21

Explain how to prove that oxygen is released during photosynthesis.

Answer 21

Study figure 10.11 on page 183

Question 22

State the uses of iron in plants, as well as its deficiency effects.

Answer 22

• Needed for chlorophyll synthesis.
• A constituent of electron carriers.
• Needed for formation of some enzymes.

Deficiency: yellowing of new upper leaves ( chlorosis )

Question 23

State the uses of Mg in plants, as well as the deficiency effects.

Answer 23

• Required for chlorophyll formation.
• It acts as an enzyme activator.
• Forms part of the middle lamellae in plants cells.

Deficiency: Yellowing of older leaves will occur ( chlorosis )

Question 24

State the uses of Phosphates in plants, as well as the deficiency effects.

Answer 24

• Is a macro - nutrient : Uses it as phosphates.
• Used to synthesise nucleotides which form nucleic acids.(RNA DNA
• Used for high energy compounds like ATP.
• A component of cell membranes in the form of phospholipids.

Deficiency: stunted growth, especially the roots. Brown areas oocur on leaves.

Question 25

State the uses of nitrates in plants, as well as the deficiency effects.

Answer 25

- Macro-nutrient: used as nitrates. - Required for amino acid synthesis. - Used to synthesise chorophyll. - Used to synthesise of nucleotides which form nucleic acids. - Some plant hormones like auxin contain nitrogen. Deficiency: Yellowing of all leaves and stunted growth.

Question 26

State the uses of K in plants, as well as its deficiency effects. ( this is the most difficult one.)

Answer 26

- Required for flowers, fruit and seed formation. Defect: No food. No beauty, nor new life.

Question 27

Explain the uptake of ions into root hairs by active transport

Answer 27

- Mineral ions are taken into root hairs by active transport - There is a low concentration in the soil and a high concentration in the root hair cell - Mineral ions are taken up against the concentration gradient - Energy is required for this - Energy is supplied by the hydrolysis of ATP - Carrier proteins in the CSM are responsible for binding with the ion and carrying it onto the cell

Question 28

Define photosynthesis

Answer 28

Photosynthesis is a method of nutrition in green plants by trapping light energy in chlorophyl and producing organic substancees (glucose) by using water and carbon dioxide with oxygen as a byproduct

Question 29

Write a balanced chemical equasion for photosynthesis

Answer 29

6CO2 + 6H2O -> 6O2 + C6H12O6

Question 30

Name the sources of carbon dioxide for photosynthesis, and how it enters into the leaf

Answer 30

- 0,04% of the air is carbon dioxide - Carbon dioxide enters the leaf by diffusion - Enters through the stomata - Diffuses into the air spaces - Then diffuses into mesophyll cells - Absorbed by chloroplasts and trapped by chlorophyl

Question 31

Name the sources of water for photosynthesis, and also how it enters the leaf

Answer 31

- Water is absorbed from the soil into the root by osmosis - Travels through the epidermis, cortex and endodermis into the xylem - Water travels up the stem xylem into the leaf xylem - Water then travels to its destination through the three pathways (later explained in detail in chapter 13)

Question 32

Describe the structure of a chloroplast

Answer 32

- Surrounded by a double membrane - Inside there is a membrane network called the thylakoids - Thylakoids are arranged into a large number of flattened piles called the grana - Chlorophyll is embedded in the granum-thykaloid membranes - Between the grana is an aqueous liquid which may contain starch grains and lipid droplets - This part is called the stroma

Question 33

Name the two phases of photosynthesis

Answer 33

- Light reaction phase | - Dark reaction phase (Calvin cycle)

Question 34

Explain what happens the first phase of photosynthesis

Answer 34

- Occurs in the grana thylakoid of chloroplasts - Light dependent - Light energy is absorbed by chlorophyll - Light energy converted into chemical energy - Chemical energy used to produce ATP from ADP and phosphates (photophosphorylation) - Energy also used to split water molecules into hydrogen ions and oxygen - Hydrogen ions are added to NADP, forming NADPH2 - Oxygen diffuses into air spaces and from there through the stomata into the air - ATP and NADPH2 move to stroma for dark reaction phase

Question 35

Explain what happens during the Calvin cycle

Answer 35

- Occurs in the stroma of chloroplasts - Occurs in light or dark, therefore light independent - Requires a continuous supply of ATP and NADPH2 from the first phase - ATP releases energy and NADPH2 releases hydrogen ions - Reduction of carbon dioxide takes place when hydrogen ions are bonded to carbon dioxide by the released energy - This forms glucose (C6H12O6)

Question 36

Name the two products which are returned to the grana after being used during the dark reaction phase

Answer 36

- ADP (from ATP) | - NADP+ (from NADPH2)

Question 37

Describe the uses of glucose in green plants

Answer 37

- Energy source for respiration - Changed into sucrose for translocation in phloem sieve tubes - Changed to insoluble starch for storage - Changed into cellulose to build cell walls - Changed into oils to store in seeds - Converted into amino acids for growth and repair - Converted into chlorophyll to trap light energy - Converted into different vitamins

Question 38

Define a limiting factor

Answer 38

- Any factor which limits the rate of a process | - when it is in shortage or excess

Question 39

Describe light as a limiting factor

Answer 39

- Photosynthesis requires light - The rate of the photosynthesis increases with light intensity - Increases until the optimum light intensity is reached - At this point the rate of photosynthesis is maximum - Further increase in light intensity will not increase the rate any more

Question 40

Describe carbon dioxide as a limiting factor

Answer 40

- Photosynthesis requires carbon dioxide - Low carbon dioxide levels = low rate of photosynthesis - More carbon dioxide means faster photosynthesis - Increases until an optimum is reached - At this point the rate of photosynthesis is maximum

Question 41

Describe temperature as a limiting factor

Answer 41

- Plants function best at optimum temperatures (20-30ºC) - Rate of photosynthesis increases with temperature, until an optimum is reached - A further increase in temperature can cause a drop in the rate of photosynthesis, because enzymes denature at high temperatures. And yes, enzymes are responsible for photosynthesis - At low temperatures enzymes are less active meaning a lower rate of photosynthesis

Question 42

Why does plant productivity increase in greenhouses?

Answer 42

- The environment can be controlled | - Optimum conditions can be reached to maximise the yield

Question 43

Explain how light intensity can be controlled in greenhouses

Answer 43

- Position the greenhouse to receive maximum light - Artificial lights supply additional light - Too strong light can be reduced with blinds - Reflectors inside the greenhouse can reflect light directly onto plants

Question 44

Explain how carbon dioxide concentration can be controlled in greenhouses

Answer 44

- Can be increased by burning fossil fuels - Can be increased using bottles of carbon dioxide - Ventilators allow fresh air with CO2 to enter

Question 45

Explain how humidity can be controlled in greenhouses

Answer 45

- Sprinkler systems give a continuous supply of water to plants - Humidifiers can be used to reduce transpiration

Question 46

Explain how temperature can be controlled in greenhouses

Answer 46

- Increased by heaters or burning fossil fuels | - Decreased using fans