Topic 6 - Plants and Photosynthesis Flashcards
What is photosynthesis?
An endothermic reaction that uses light energy to convert carbon dioxide and water into glucose and water
What is glucose used for in plants
- It is used as a ‘food source’ in plants
- it is used in respiration to release energy
- it is used to make larger, more complex molecules such as cellulose which makes up the cell wall
- excess glucose is converted into starch for storage
Where does photosynthesis happen?
-It takes place in the chloroplasts of plant cells
- the chloroplasts contain chlorophyll which absorbs the light energy
- it happens in the leaves of all green plants
Why are plants so important for the ecosystem
- they are photosynthetic organisms that are the main producers of biomass and therefore food
- they store energy which is transferred to organisms that eat it and works its way up the food chain
Equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
How does sunlight exposure affect photosynthesis
- Plants exposed to more sunlight can photosynthesise longer
- This means they produce more glucose because glucose is a product of photosynthesis
What is a limiting factor
- A factor that stops photosynthesis from happening faster
- If a factor is too high or low it will become the limiting factor
What are the 3 limiting factors?
- Light intensity
- carbon dioxide concentration
- temperature
Effect of light intensity
- up to a certain point, as light intensity increase the rate of reaction increases as well
- this is because light provides the energy needed for photosynthesis
- after a certain point, the graph will start to plateau and increasing L.I won’t make a difference
- now another factor is limiting factor
effect of carbon dioxide concentration
- up to a certain point, as CO2 intensity increases the rate of reaction increases as well
- this is because CO2 is a reactant needed for photosynthesis
- after a certain point, the graph will start to plateau and increasing CO2 concentration won’t make a difference
- now another factor is a limiting factor
effect of temperature
- up to a certain point, as temp increases the rate of reaction increases as well
-enzymes work more quickly and the molecules move faster due to more kinetic energy - at the optimum temperature, something else is the limiting factor
- after the optimum temperature, the rate of reaction decreases as the enzyme begins to denature
How do you test a leaf for starch
- place leaf in beaker with boiling water to melt waxy cuticle
- put leaf in boiling tube and put ethanol, to remove the chlorophyll from the leaf: this decolourises it
-put leaf back in boiling water to soften it
-lay leaf on tile and flood with iodine, to see where the starch is
test for starch
iodine changes colour from brown- orange to blue-black
inverse square law
light intensity = 1/ distance²
translocation
movement of organic solutes ( e.g : sucrose ) from a source to a sink
through the phloem
what is the organic molecules used for
1) used for respiration instantly to release energy
2) make larger molecules ( e.g : starch) for storage
Phloem
- transports food substances ( e.g : sucrose ) made in the leaf
- transports it up AND down the plant ( it goes from leaves to roots and vice versa)
- columns of elongated living cells with small pores in end walls
- requires energy from respiration
- translocation
transpiration
the loss of water from a plant’s surface
How plant loses water
- evaporation of water from inside the leaf
- followed by diffusion of water vapour from the stomata
Xylem
- carry water and mineral ions
- only transports it UP the plant
-from roots to the stem and leaves - made of dead cells joined together with NO end walls
- strengthened by lignin
Transpiration stream
movement of water and mineral ions through a plant from the roots to the leaves to obtain more water for photosynthesis
Process of transpiration
- water evaporates from cells into air spaces within the leaf
-water then diffuses out of the leaf through stomata
-this creates a shortage of water in the leaf - more water is drawn up from the rest of the plant through the xylem vessels to replace it
- this means more water is drawn up from roots, so there is a constant transpiration stream
Root hair cells
- cells on the surface of plant roots that grow into hairs which stick out into the soil
- this increases the surface area for absorbing water and mineral ions
What 3 factors affect transpiration rate
- light intensity
- temperature
-air flow
how does light intensity affect transpiration
- the greater the light intensity, the greater the transpiration rate
- as it gets darker the stomata closes, as the plant can no longer photosynthesise
- this means that when the stomata are closed water can’t escape
how does temperature affect transpiration
- the warmer it is the faster the rate of transpiration
- water particles have more kinetic energy and so diffuse out of the stomata faster
how does air flow affect transpiration
- the better the air flow, the faster the rate of transpiration
- if it is windy, the water vapour is swept away from the leaf
- this means there is al ow concentration of water outside the leaf compared to outside it
- this maintains a high concentration gradient, which increase the rate of diffusion of water out of the leaf
what do you use to measure rate of transpiration
potometer
what are guard cells
two guard cells surround each stoma to help open and close them
what happens to the guard cells when the plant has lots of water
- guard cells fill with water and become turgid
- this opens the stomata so gases can be exchanged for photosynthesis
what happens to the guard cells when the plant is short of water
- water moves out of the guard cells and they become flaccid
- this closes the stomata so gases can’t be exchanged for photosynthesis
how does the guard cells respond to lack of light
it closes to save on water without losing out on photosyntheis
how is the upper part of the leaf adapted for photosynthesis
upper epidermis covered with a thick waxy cuticle layer, to reduce water loss by evaporation
- upper epidermis cells are transparent to allow light to pass through to the palisade layer
how is the palisade part of the leaf adapted for photosynthesis
- cells in palisade mesophyll contain lots of chloroplasts. contain lots of chlorophyll to absorb light energy needed
- xylem and phloem form a network of vascular bundles, which also supports the structureh
how is the lower part of the leaf adapted for photosynthesis
- lower epidermis is full of holes called stomata which let CO2 and water diffuse directly in and out of the leaf
- air spaces in spongy mesophyll increase the rate of diffusion of gases through the leaf due to increased S.A
- leaves are broad, so there is a large S.A exposed to light
how are plants in dry extreme habitats adapted for photosynthesis
- they have small leaves or spines to reduce S.A for water loss by evaporation
- thicker waxy cuticle to further reduce water loss by evaporation
- curled leaves reduce air flow close to leave which reduces rate of transpiration
- stems of some plants are thick and fleshy to help store more water
- stomata sunk in pits to reduce air flow in same way as curled leaves/hairs
what do plants need to do?
plants need to detect and respond to stimuli in order to survive
What is auxin?
a plant hormone that controls growth near the tips of roots and shoots
phototropism
plant growth in response to light
gravitropism
plant growth in response to gravity
shoots
- auxins stimulate growth in shoots
- positively phototropic
- negatively gravitropic
roots
- auxins inhibit growth in shoots
- negatively phototropic
- positively gravitropic
how do shoots respond to light?
- due to the light stimulus detected, auxins will diffuse down the concentration gradient from the tip
- diffuse unevenly and accumulate more of shady side
- this cause the shoot to bend away from the shady side, closer to light
how do shoots respond to gravity?
- due to the gravity stimulus detected, auxins will diffuse down the concentration gradient from the tip
- diffuse unevenly and accumulate more on lower side
- this cause the shoot to bend away from the lower side, upwards and away from gravity
how do roots respond to light?
- due to the light stimulus detected, auxins will diffuse down the concentration gradient from the tip
- diffuse unevenly and accumulate more of shady side
- this cause the shoot to bend towards the shady side, away from light
how do roots respond to gravity?
- due to the gravity stimulus detected, auxins will diffuse down the concentration gradient from the tip
- diffuse unevenly and accumulate more on lower side
- this cause the shoot to towards the lower side, therefore towards gravity
Auxins - use for selective weedkillers
-spraying high concentrations of auxins disrupts plants’ normal growth patterns.
- because weeds have broader leaves than grass they have a greater S.A and so weeds take up more auxins and are killed, but the grass survives
Auxins - rooting powder
- rooting powder can be added to cuttings to stimulate them to grow roots
- they contain auxins which controls the roots growth
- they will start growing rapidly as new plants
- this enables people to produce lots of clones of desirable plants
What are gibberellins?
a plant hormone that stimulates seed germination ( growth of seed -> plant) and flowering
Gibberellins - controlling seed germination
- most seeds won’t germinate until certain conditions are met ( e.g : warmth)
- they only germinate at certain times of the year
- exposure to gibberellins can cause the seed to germinate at times of the year they normally wouldn’t
- it makes sure seeds in a batch all germinate at the same time
Gibberellins - flower formation
- gibberellins can be used to make plants flower earlier than they would
or under conditions that they usually wouldn’t - can be used to reduce flower formation
- improves fruit quality
gibberellins - seedless fruit
- fruit normally grows on flowering plants that have been pollinated, which also makes the seed grow
- if gibberellin is added, the fruit will grow but the seeds won’t
What is ethene?
a plant hormone produced by aging parts of the plant that causes the fruit to ripen
ethene - Commercial use
- used to speed up the ripening of fruits
- they can be picked while its still unripe which make it firmer and less easily damaged when transported
- ethene gas is added on the way to the supermarket so it’s perfect just as it reaches the supermarket
