Chapter 10 Photosynthesis Flashcards
1
Q
State the function of the upper epidermis of a leaf
A
- Transparent cells (no chloroplasts) which covers the upper surface of the leaf
- Allows light to pass through
- Protect the inner cells
- Produce the cuticle
2
Q
State the function of the cuticle on a leaf
A
- Waxy, waterproof layer covering the upper epidermis of the leaf
- Reduces water from evaporating from the leaf
3
Q
State the function of the lower epidermis of the leaf
A
- Transparent, covers the lower surface of the cell
- Allows light to pass through, protects inner cells and sometimes also produces a cuticle
4
Q
Name the different layers of which a leaf consists
A
- Upper epidermis
- Lower epidermis
- Cuticle
- Mesophyll layer
- Vascular bundles
- Stomata
5
Q
Describe the mesophyll layer?
A
- 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.
6
Q
What are vascular bundles or veins?
A
- 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.
7
Q
Describe the stomata and its fuctions.
A
- 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.
8
Q
Study diagram on page 177
if still uncertain what to do, read below.
A
hi…. i’m Bob. I’m a goldfish. A gold fish has a memory of…hi….i’m bob.
9
Q
Discuss the ways in which the structure of a leaf has adapted to carry out photosynthesis.
A
- 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.
10
Q
Describe how the upper and lower epidermis layers are adapted to support photosynthesis
A
- Tranparent to allow light to pass to the mesophyll layer
11
Q
Describe how the palisade mesophyll layer in a leaf is adapted to carry out photosynthesis
A
- 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
12
Q
Describe how the spongy mesophyll layer is adapted to carry out photosynthesis
A
- 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
13
Q
Describe how chloroplasts are adapted to carry out photosynthesis
A
- Can move within the mesophyll to the light
- Can move away from intense light to avoid damage
14
Q
Describe how stomata are adapted to assist in photosynthesis
A
- Holes in the lower epidermis for gases to enter and leave during gaseous exchange
15
Q
Describe how xylem and phloem assist in the process of photosynthesis
A
- 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
16
Q
Name the steps in carrying out starch tests on leaves
A
Take a green leaf which was exposed to sunlight for a few hours (where glucose was produced and changed into starch for storage)
- Boil the leaf until flabby (to destroy cell walls, membranes, cytoplasm and enzymes for iodine penetration
- 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)
- Rinse the leaf in hot water (to soften it which is hardened by alcohol)
- 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
17
Q
Describe how starch would be removed from a plant
A
- 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
18
Q
Describe how one would show that light is essential for photosynthesis
A
- 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
19
Q
Describe how one would show that carbon dioxide is necessary for photosynthesis
A
- 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
20
Q
Describe how one would show that chlorophyll is essential for photosynthesis
A
- 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
21
Q
Explain how to prove that oxygen is released during photosynthesis.
A
Study figure 10.11 on page 183
22
Q
State the uses of iron in plants, as well as its deficiency effects.
A
- Needed for chlorophyll synthesis.
- A constituent of electron carriers.
- Needed for formation of some enzymes.
Deficiency: yellowing of new upper leaves ( chlorosis )
23
Q
State the uses of Mg in plants, as well as the deficiency effects.
A
- 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 )
24
Q
State the uses of Phosphates in plants, as well as the deficiency effects.
A
- 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.
25
State the uses of nitrates in plants, as well as the deficiency effects.
- 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.
26
State the uses of K in plants, as well as its deficiency effects.
( this is the most difficult one.)
- Required for flowers, fruit and seed formation.
Defect: No food. No beauty, nor new life.
27
Explain the uptake of ions into root hairs by active transport
- 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
28
Define photosynthesis
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
29
Write a balanced chemical equasion for photosynthesis
6CO2 + 6H2O -> 6O2 + C6H12O6
30
Name the sources of carbon dioxide for photosynthesis, and how it enters into the leaf
- 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
31
Name the sources of water for photosynthesis, and also how it enters the leaf
- 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)
32
Describe the structure of a chloroplast
- 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
33
Name the two phases of photosynthesis
- Light reaction phase
| - Dark reaction phase (Calvin cycle)
34
Explain what happens the first phase of photosynthesis
- 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
35
Explain what happens during the Calvin cycle
- 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)
36
Name the two products which are returned to the grana after being used during the dark reaction phase
- ADP (from ATP)
| - NADP+ (from NADPH2)
37
Describe the uses of glucose in green plants
- 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
38
Define a limiting factor
- Any factor which limits the rate of a process
| - when it is in shortage or excess
39
Describe light as a limiting factor
- 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
40
Describe carbon dioxide as a limiting factor
- 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
41
Describe temperature as a limiting factor
- 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
42
Why does plant productivity increase in greenhouses?
- The environment can be controlled
| - Optimum conditions can be reached to maximise the yield
43
Explain how light intensity can be controlled in greenhouses
- 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
44
Explain how carbon dioxide concentration can be controlled in greenhouses
- Can be increased by burning fossil fuels
- Can be increased using bottles of carbon dioxide
- Ventilators allow fresh air with CO2 to enter
45
Explain how humidity can be controlled in greenhouses
- Sprinkler systems give a continuous supply of water to plants
- Humidifiers can be used to reduce transpiration
46
Explain how temperature can be controlled in greenhouses
- Increased by heaters or burning fossil fuels
| - Decreased using fans
