Biology GCSE AQA Year 9: Plants

What is the function of the cell wall?

Provides support

What is the function of the nucleus?

Controls cell activities

What is the function of chloroplast?

Absorbs light energy for photosynthesis

What is the function of the permanent vacuole?

Contains cell sap

What is the function of the cell membrane?

Controls entry in and out of the cell

What is the function of cytoplasm?

Where chemical reactions take place

What is the function of mitochondria?

Releases energy in respiration

What is the function of ribosomes?

Where protein synthesis occurs

What is a tissue?

A group of cells with similar structure and function

What is the function of the epidermal tissues?

. Covers the plant and protects it

. Transparent so allows light to pass through to the palisade layer

. Secretes a waxy substance (waxy cuticle) that waterproofs the surface to reduce water loss

What is the function of the palisade mesophyll?

. Where most photosynthesis occurs as cells contain many chloroplasts

. Cells are found near the top of the leaf and are elongated to absorb as much light energy as possible

What is the function of the spongy mesophyll?

. Irregular shaped cells so have large air spaces which allow gases to diffuse easily and quickly through the leaf from the stomata to the palisade layer and back

. Contains some chloroplasts so some photosynthesis occurs

What is the function of the xylem?

Transports water and dissolved mineral ions from the roots to leaves and stems

What is the function of the phloem?

Carries dissolved sugars from the leaves to all parts of the plant for immediate use or storage.

What is the function of the meristem tissue?

. Located at growing tips of roots and shoots

. Made of cells that divide quickly and can differentiate into many different types of cells

What is the difference between stoma and stomata?

stoma = singular

stomata = plural

What are the stomata?

. Holes within the epidermis tissues

. Mainly found on the lower epidermis

. Allow carbon dioxide and oxygen to diffuse in and out of the leaf

. Water can also leave via the stomata

. They are opened and closed by guard cells

What is the leaf?

A plant organ

What is an organ?

Collection of tissues that work together to perform a particular function

Name 3 plant organs and their functions

. Leaves - carry out photosynthesis

. Roots - absorb water and minerals from the soil

. Stems - support the leaves and flowers

What is photosynthesis?

An endothermic reaction in which energy is transferred from the environment to the chloroplasts by light

What is an endothermic reaction?

A reaction that takes in energy from the surroundings (so the temperature of the surroundings decreases)

What is an exothermic reaction?

A reaction that transfers energy to the surroundings (so the temperature of the surroundings increases)

Where does photosynthesis occur?

organ: leaf

cell type: mostly palisade cells

organelle: chloroplast

What does chloroplast contain and how does it aid the process of photosynthesis?

. Contains chlorophyll which absorbs light energy

. Chlorophyll is a green pigment found in the chloroplasts of plants and some algae

Describe how the 2 reactants in photosynthesis reach the organelle where the reaction takes place

. CO2 diffuses down a conc gradient, through the stomata and the air spaces, into the palisade mesophyll cells through the cell wall, through the cytoplasm, and into the chloroplasts

. Water enters the root hairs by osmosis, down a conc gradient, through a partially permeable membrane

. It then passes across the root, from cell to cell by osmosis. It also seeps between the cells.

. Water is drawn up the xylem vessels because transpiration is constantly moving water from the top of them

. The water then moves by osmosis, down a conc gradient, through a partially permeable membrane, into the palisade mesophyll cells, and enters the chloroplasts

What is the word equation for photosynthesis?

Water + Carbon Dioxide -> Oxygen + Glucose

What is the balanced symbol equation for photosynthesis?

6 H2O + 6 CO2 -> 6 O2 + C6H12O6

How do plants use glucose?

. Used for respiration

. Converted into insoluble starch for storage (so it won't affect osmosis in cells)

. Used to produce fat or oil for storage (mostly for energy storage in seeds)

. Combined with nitrate ions absorbed from the soil to produce amino acids for protein synthesis

. Used to produce cellulose, which strengthens the cell wall

What is the function of a physical defense response?

to resist invasion of microorganisms

Name 3 physical plant defence responses and what they protect against

. Cellulose cell wall - protects against pathogens entering cells

. Tough waxy cuticle on leaves - protects against pathogens invading leaf tissue

. Layers of dead cells around stems which fall off (e.g bark on trees) - protects against pathogens attacking the stem (as when dead cells are lost, the pathogens fall off as well)

Name 2 chemical plant defence responses and what they protect against

. Antibacterial chemicals (e.g mint, garlic) - protect against bacterial growth

. Poisons (e.g foxgloves) - protect against herbivores eating the plant

Name 3 mechanical adaptations and what they protect against

. Thorns and hairs - protect against herbivores eating the plant and prevents insects from laying their eggs there

. Leaves which droop or curl when touched (e.g mimosa) - protect against herbivores eating the plant (dislodges any herbivores on the leaves, reduces the SA of the plant, and frightens animals)

. Mimicry to trick animals (e.g passionflower leaves have a pattern that looks like eggs are present. Some plants also mimic unhealthy plants.) - protects against herbivores eating the plant and insects laying eggs on the leaves

How do you test a leaf for starch?

. boil it for up to a minute

. put in tube of ethanol in hot water until ethanol turns green and leaf has lost colour

. dip in hot water

. place on white tile and add iodine solution

What are the safety considerations for testing a leaf for starch?

. Ethanol is highly flammable - ensure there are no naked flames around it

. Ethanol must be disposed in a waste container, not down the sink

. Iodine can stain hands and clothing

. Wear eye protection

Why do we boil the leaf in water when testing a leaf for starch?

to destroy waxy cuticle and break cell walls in leaf cells

Why do we not use a bunsen burner / turn it off before putting leaf and ethanol in the water when testing a leaf for starch?

Ethanol is very flammable

Why do we leave the leaf in ethanol when testing a leaf for starch?

Removes the green colour (chlorophyll) from the leaf so we can see the colour of the iodine solution better.

Why do we dip the leaf in hot water after the ethanol when testing a leaf for starch?

softens leaf

Why do we add iodine to the leaf when testing a leaf for starch?

shows us if the leaf contains starch

What is the 'law of limiting factors'?

When a process depends on 2 or more factors, the rate of that process is limited by the factor which is in shortest supply

What factors affect the rate of photosynthesis?

. Light intensity

. Carbon dioxide concentration

. Temperature

. Amount of chlorophyll

Imagine a pond weed growing under a test tube in a beaker of water (see notes for diagram). How could you measure the rate of photosynthesis?

. Bubbles of oxygen are being produced as the plant cells photosynthesise

. Rate = number of oxygen bubbles produced in a set time OR volume of oxygen bubbles produced in a set time

Describe a graph showing the affect of light intensity on the rate of photosynthesis

. When there's no light, the rate of photosynthesis is 0

. In very low light levels, there's a low rate of photosynthesis

. As light intensity reaches x (read value of light intensity when r of p plateaus), the rate of photosynthesis plateaus at y (read value of r of p when it plateaus)

Explain a graph showing the affect of light intensity on the rate of photosynthesis

. Light is required for photosynthesis. Without light, photosynthesis cannot occur and the rate of photosynthesis is 0.

. As light intensity increases, the plant cells start to photosynthesise at a low rate

. The higher the light intensity, the higher the rate of photosynthesis. This shows that here, the light intensity is the limiting factor.

. When the rate of photosynthesis plateaus, this means that another factor has become the limiting factor (e.g temperature or CO2 conc)

As the distance of the light from the plant increases, what happens to the light intensity?

. Light intensity decreases

. Inverse relationship; as one goes up, the other goes down

What is the equation for light intensity and distance?

. the Inverse Square Law

. light intensity ∝ 1 / distance²

. ∝ means proportional

If you double the distance between the light and the plant, what happens to light intensity?

It falls to a quarter of what it was

Describe a graph showing the affect of carbon dioxide conc on the rate of photosynthesis

. If the CO2 conc is 0, so is the rate of photosynthesis

. In very low CO2 concs, there's a low rate of photosynthesis

. As CO2 conc increases, so does the rate of photosynthesis

. When CO2 conc reaches x (read value of CO2 conc where RofP plateaus), the rate of photosynthesis plateaus at y (read value of RofP when it plateaus)

Explain a graph showing the affect of carbon dioxide conc on the rate of photosynthesis

. CO2 is required for photosynthesis. Without CO2, photosynthesis cannot occur and the rate of photosynthesis is 0.

. As CO2 conc increases, the plant cells start to photosynthesise at a low rate

. The higher the CO2 conc, the higher the rate of photosynthesis. This shows that here, the CO2 conc is the limiting factor.

. When the rate of photosynthesis plateaus, this means that another factor has become the limiting factor (e.g light intensity or temperature)

Describe a graph showing the affect of temperature on the rate of photosynthesis

. At very low temperatures, there is a low rate of photosynthesis

. As temp increases, so does the rate of photosynthesis

. When temp reaches x (read value of temp at peak), this is the optimum temp and the rate of photosynthesis reaches y (read value of RofP at peak) which is its peak.

. As the temp increases above the optimum temp, the rate of photosynthesis falls rapidly to 0.

Explain a graph showing the affect of temperature on the rate of photosynthesis

. When temp is low, the reactants have low levels of kinetic energy and the rate of photosynthesis is low

. As temp increases, the plant cells start to photosynthesise at a faster rate as the reactants have more kinetic energy

. At the optimum temp, the rate of photosynthesis is highest

. If the temp continues to increase, the enzymes catalysing the reaction start to denature and the rate of photosynthesis falls to 0

Why are farmers concerned with crop yield?

. Human population growth

. Food security

. Profit

Why are greenhouses useful

Can control limiting factors to get the fastest rates of photosynthesis so plants grow faster

How are greenhouses balanced with economics?

. Need money for:

. Electricity and gas to change temperature and light levels

. Monitoring equipment and computers to maintain conditions

. However more automated so fewer staff are needed so fewer salaries to pay