topic 6 - plant structures and functions

describe what a photosynthetic organism is

main producer of food and biomass (e.g. grass)

describe what type of reaction photosynthesis is

• endothermic reaction

• uses light energy

• to react carbon dioxide and water

• to produce glucose and oxygen

what are the products of photosynthesis

glucose and oxygen

what are the reactants of photosynthesis

carbon dioxide and water

describe how water and mineral ions enter a plant

• water molecules are absorbed into root hair cells by osmosis

• mineral ions are absorbed into root hair cells by active transport

“describe and explain how water moves through a plant”

• hollow xylem vessels

• made of dead cells

• strengthened by lignin

• carry water and mineral ions

• from roots to leaves

• by transpiration

• where water evaporates from leaf’s surface

“describe and explain how sucrose moves through a plant”

• phloem sieve tubes

• made from living cells

• carries sucrose in water

• from leaves to roots

• by translocation

describe how temperature effects the rate of photosynthesis

• photosynthesis relies on enzyme action

• increasing temperature increases rate of photosynthesis

• as temperature increases past optimum, rate of reaction will decrease and eventually halt

• as high temperatures can cause the enzymes to denature

• meaning the reaction is not catalysed

describe how light intensity effects the rate of photosynthesis

• light provides energy for the photosynthesis reaction

• light intensity is directly proportional to the rate of reaction

• as an increase in energy will increase the rate of reaction

describe how carbon dioxide concentration effects the rate of photosynthesis

• carbon dioxide is a reactant in the photosynthesis reaction

• carbon dioxide concentration is directly proportional to the rate of reaction

• as an increase in carbon dioxide concentration will increase the rate of reaction

explain how light intensity and rate of photosynthesis are directly proportional

• as light intensity increases the rate of photosynthesis also increases

• this is because photosynthesis is an energy requiring reaction (endothermic)

• more light energy will increase the rate at which oxygen is given off

explain how distance from light source and rate of photosynthesis are inversely proportional

• as the distance increases, light intensity decreases

• this is because as the distance away from a light source increases, light energy becomes spread over a wider area

• decreasing the light intensity

• meaning there is less light to provide energy for photosynthesis

state the inverse square law equation

1/(distance)²

core prac - investigating the effect of light intensity on the rate of photosynthesis (METHOD)

• set up and LED lamp and a ruler pointing away from

• make 5 tubes containing the same volume of water and hydrogencarbonate indicator

• add the same number of plant to each test tube

• cover one test tube with foil so it doesn’t receive any light (control)

• set the test tubes up at different distances away from the lamp

• leave for a fixed amount of time

• remove the foil from the control

• measure the colour of each solution against the hydrogencarbonate indicator scale

core prac - investigating the effect of light intensity on the rate of photosynthesis (RESULTS)

• test tubes closer to the lamp will have a darker purple colour as they have a lower concentration of carbon dioxide

• this is due to the increased rate of photosynthesis caused by increased light intensity

• which has caused more carbon dioxide to be used as a reactant

state what positive phototropism is

when an object bends towards a light source

state what negative phototropism is

when an object bends away from a light source

state what positive gravitropism is

an objecting bending towards the direction of gravity

state what negative gravitropism

a plant growing away from the ground

state what types of tropism occur in the roots of plants

• positive gravitropism

• negative phototropism

state what types of tropism occur in the stems of plants

• negative gravitropism

• positive phototropism

explain how auxins affect plant growth and development in the shoots/stems

1. the tip of the shoot produces auxins

2. auxins are transported towards the shaded side of the shoot tip and diffuse down the shaded side

3. auxins in the shoot cause cell elongation

4. causing the positive phototropism in the shaded side of the shoot tip (shoot tip bends towards the light source)

explain how auxins affect plant growth and development in roots

• the root produces auxins

• gravity pulls the auxins to the bottom of the root

• auxins in the root inhibit cell elongation

• causing positive gravitropism (root bends down towards gravity)

explain how the large surface area of root hair cells is an adaptation to absorb water and mineral ions

it allows for an increased rate of osmosis and active transport

explain how the large amount of mitochondria in root hair cells is an adaptation to absorb water and mineral ions

• the mitochondria allow for aerobic respiration

• which releases lots of energy for active transport and osmosis

• of ions and water molecules into plant roots

explain how xylem vessels are adapted to their function in plants

• tubes are made of dead cells (no cytoplasm or organelles) to allow water to flow through

• enhanced with lignin

• to make the cell walls stronger

• so they’re less susceptible to damage

• by changes in water pressure

explain how sieve tubes in phloem vessels are adapted to their function in plants

• made of living cells

• cells have no nuclei

• tubes have perforated ends so cell cytoplasm connects together

• sieve tubes have companion cells attached to provide energy for translocation

• sucrose is transported through the cytoplasm of the sieve tubes

explain how companion cells in phloem vessels are adapted to their function in plants

• the transport of sucrose and other substances requires energy

• companion cells attached to sides of sieve tubes provide energy for sieve tubes

• through containing large amounts of mitochondria

• which release energy through aerobic respiration

explain transpiration process

• water is drawn through xylem in continuous transpiration stream

• from roots to leaves via stem

• to replace water lost through transpiration

• strong cohesion causes water in xylem to create a continuous column

• transpiration causes tension on water column

• causing stream to be pulled out of xylem vessels and evaporated on leaf’s surface

state what the function of the stomata are in transpiration

• the size of the stomatal opening is used by the plant to control the rate of transpiration

• it therefore limits the levels of water loss from the leaf

describe how sucrose is transported around the plant by translocation

• sucrose are transported around the plant through phloem vessels

• the sucrose is transported within cytoplasm in sieve tubes around the plant

• energy for translocation in sieve tubes is provided by companion cells

explain the effect of light intensity on the rate of water uptake by plants (guard cells)

• guard cells are responsive to light intensity

• increasing light intensity causes the guard cells to become turgid

• this causes the stomata to open

• which increases rate of transpiration

• causing root hair cells to absorb more water from the soil

• to replace water lost

explain the effect of air movement on the rate of water uptake by plants

• increased air movement = increased rates of transpiration

• air movement moves saturated air away from the leaves

• this places more tension on the water transpiration stream in the xylem vessels

• causing increased rates of transpiration and evaporation of water molecules on the leaf’s surface

• causing increased water absorption in root hair cells by osmosis to replace the lost water

explain the effect of temperature on the rate of water uptake by plants

• increasing temperature increases rate of water uptake

• as more water molecules evaporate from the leaf surface

• placing excess tension on the continuous water transpiration stream in xylem vessels

• causing increased rates of transpiration

• which causes root hair cells in the plant roots to absorb more water through osmosis

• to replace water lost

explain how to calculate rate of transpiration

• use a bubble potometer to measure the amount of time it take for an air bubble to move a fixed distance towards the plant

• use the equation: rate = distance/time to find the rate of transpiration

explain how the structure of a leaf is adapted for photosynthesis and gas exchange

• large surface area - take in more sunlight for photosynthesis

• thin - decrease time taken for carbon dioxide diffusion through the leaf

• stomata - allows carbon dioxide to diffuse into the leaf for photosynthesis

• guards cells - open or close stomata depending on external conditions

• xylem vessels - transport water from the roots to the leaves for photosynthesis

• contains chlorophyll - absorb sunlight for photosynthesis

explain how leaf size and shape is adapted to allow plants to survive extreme environments

• in hot environments, leaf size is reduced to tiny spikes

• this reduces water loss by transpiration by reducing the surface area of the lead

explain how the waxy cuticle is adapted to allow plants to survive extreme environments

• the waxy cuticle is thicker on leaves in hot environments

• this reduces water loss by transpiration

explain how the stomata is adapted to allow plants to survive extreme environments

• in hot environments, leaves have a reduced number of stomata

• this reduces water loss by transpiration

explain how auxins are used as weed killers

• auxins are used as selective weed killers

• that negatively effect the growth of broad-leaved plants

• when the auxins are sprayed on the weeds, they cause rapid growth through cell elongation

• this growth becomes uncontrollable and leads to the weed dying as it’s exhausted all its resources

explain who uses auxins as weed killers and why

• farmers

• as they are selective

• and only target broad-leaved weeds

• and not narrow-leaved crops

explain how auxins are used in rooting powders

• the auxins in rooting powder can cause a cutting of plant to grow into a clone of the cutting

• as they encourage rapid development of roots

explain who uses auxins in rooting powders and why

• gardeners or farmers

• who want to cheaply produce a high yield of cloned plants

explain how gibberellins can cause germination

• a high concentration of gibberellins can cause seed germination

• as gibberellins promote plant growth and development

• through stimulating cell elongation

explain how gibberellins can promote flowering

• as gibberellins are responsible for growth and development in plants

• through cell elongation

• they can end seed dormancy

• and cause a plant to flower, even out of season

explain how gibberellins can cause an increase in fruit size

• gibberellins can cause cell elongation

• which makes the size of fruit bigger as its cells are more elongated

explain how gibberellins can create seedless fruits

• seeds in fruit are only created when the plant is pollinated

• gibberellins cause plant growth and development by stimulating cell elongation

• if gibberellins are used on unpollinated plants, the fruits produced won’t contain any seeds

explain who uses gibberellins and why

• gardeners or farmers

• to be able to produce fruits and plants all year round

• not just relying on the optimum external environment

explain who uses ethene and why

• food industry

• as it is easier to transport and store unripe fruits