Biology

Biology

ContentsPlant Processes

◦ Leaf structure◦ Photosynthesis

Limiting Factors Uses of Glucose

◦ Plants and Water Osmosis Osmosis in Different

Cells◦ Transpiration◦ Plant Growth and Fe

rtilisers Plant Senses and thei

r Commercial Uses

Response to Water Response to Gravity Response to Light

Biomass, Farming and Decay◦ Biomass

Pyramid of Numbers Pyramid of Biomass

◦ Intensive Farming and Organic Farming Pesticides Fertilisers Eutrophication

◦ Decay and Food Preservation

◦ Recycling of Carbon and Nitrogen

Key Words

PLANT PROCESSES

Leaf structurePhotosynthesis

Limiting FactorsUses of Glucose

Plants and WaterOsmosisOsmosis in Different Cells

TranspirationPlant Growth and Fertilisers

Plant Senses and their Commercial UsesResponse to WaterResponse to GravityResponse to Light

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The Leaf Structure

The Leaf It is the organ of photosynthesis The waxy cuticle is a waterproof

layer that cuts down the loss of water by evaporation

The epidermis allows sunlight to pass through to the palisade cells where most of photosynthesis takes place

It contains lots of chloroplasts which contains chlorophyll to absorb sunlight

The spongy layer contains rounded cells with lots of air spaces to allow carbon dioxide to circulate and reach the palisade cells

The leaf vein contains xylem and phloem tubes which supply water and glucose throughout the plant

At the bottom are stomata which open and close to let carbon dioxide in and water vapour and oxygen out

Guard cells surround the stomata

and control their opening and closing When there is a short supply of

water the guard cells become flaccid and less curved. This closes the stomata to save on water

When there is a lot of water the guard cells become turgid and curved. The stomata are open and allows the water to escape

For maximum efficiency, the plant:◦ Leaves are flat with a large surface

area to absorb as much sunlight as possible

◦ They are thin to allow carbon dioxide to reach the inner cells easily

◦ They have plenty of stomata in the lower skin

◦ They have plenty of veins to support the leaf and carry substances around the plant

Leaves and Photosynthesis

A leaf has an upper and lower epidermis covered with a waxy cuticle

The spongy mesophyll and palisade cells contain chloroplasts Guard cells surround the stomata Leaves are adapted for efficient photosynthesis by having a

large surface area, being thin and having veins Photosynthesis occurs mainly in the leaves Water enters the root hairs by osmosis Carbon dioxide enters and oxygen leaves by diffusion through

stomata The leaf is very efficient in photosynthesising because it has a

large internal surface area, internal air spaces and many chloroplasts in the palisade layer

There are three main limiting factors that affect the rate of photosynthesis. They are:◦ Light◦ Carbon dioxide◦ Temperature

Limiting FactorsLight• If the light intensity is

increased, photosynthesis will increase steadily, but only up to a certain point

• After this point, increasing the amount of light will not make any difference as it will be either the amount of CO₂ or temperature that is the limiting factor

Carbon Dioxide• If carbon dioxide

concentration is increased, photosynthesis will increase to a certain point

• Beyond this point, light or temperature become the limiting factor

Temperature• You can increase light and CO₂ as

much as possible, but the temperature must not get too cold or too hot

• A temperature of about 45°C destroys the enzymes in chloroplasts

• Usually the rate of photosynthesis is limited by the temperature being too low, as is the case for plants not normally grown in Britain

• Greenhouses help maintain a high enough temperature for optimum growth conditions

Se-ries1

Amount of Light

Rate

of P

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Se-ries1

Carbon Dioxide Concentration

Rate

of P

hoto

synt

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Series1Temperature

Rate

of P

hoto

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45°C

Uses of GlucoseSome glucose is used in respiration to obtain

energyOther uses include converting it to:

◦ Insoluble starch stored in the roots, particularly in the winter. In this form it does not cause too much water to move into the cells by osmosis, as it doesn’t contribute to the concentration inside the cells

◦ Cellulose, needed for cell walls◦ Lipids and oils are formed from glucose and stored

in seeds◦ Glucose can also be combined with other

substances, such as nitrates obtained from the oil and turned into proteins

Plants and Water Plant cells are supported by their cell walls and turgor

pressure in the cell sap Water enters the root hairs by osmosis Osmosis is the movement of water from a high concentration

to a low concentration through semi-permeable membrane A semi-permeable membrane only allows the movement of

small molecules Water moves both in and out of the root to try to even the

concentrations. Therefore we use the net movement of water Osmosis is a type of diffusion A plant must balance its water uptake and water loss Water is needed for photosynthesis, cooling and transport A leaf is adapted to reduce water loss Leaves lose water because a leaf is adapted for

photosynthesis

Osmosis Root hairs take in water by

osmosis Water moves along the cells of the

root and up the xylem to the leaf All the time the water is moving to

areas of lower water concentration Osmosis makes plant cells swell

up The water moves into the plant

cell vacuole and pushes against the cell wall making it turgid

It is useful as it gives the stem support

When there is little water the cells become flaccid as water has moved out of the cell

If a lot of water leaves the cell, the cytoplasm started to peel away from the cell wall which is called plasmolysis

The cell will behave differently in an animal cell because there is no cell wall to prevent the cell from bursting (haemolysis)

Osmosis in Different Cells

In a

Pla

ntIn

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Anim

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NormalToo Much Water Too Little Water

Transpiration Water loss from a plant is called transpiration The water evaporates and exits the leaves by diffusion Water travels from the roots, through the stem to the leaves in xylem

cells Dissolved food travels downwards in phloem cells The rate of transpiration is speeded up by a higher temperature,

more wind, a low humidity and more light More light will increase the transpiration rate because the stomata

will be open A higher temperature will increase the transpiration rate by

increasing the diffusion rate A low humidity will allow more water vapour to diffuse out of the

leaves Xylem cells are dead because they have extra lignin thickening The flow of water up the xylem to the leaves is called the

transpiration stream The transpiration stream also draws minerals into the plant as well as

water As water is lost, the transpiration stream replaces it so there is a

constant flow

Fertilisers and Plant Growth Plants need minerals in fertilisers such as nitrates,

phosphates, potassium and magnesium compounds Minerals are needed only in small quantities Nitrates are needed to make proteins for growth Phosphates are needed for root growth Potassium is needed for flower formation Magnesium is needed to make chlorophyll If minerals are missing from the soil water, the plant

shows that it is mineral-deficient Minerals are taken up from the soil water by active

transport Minerals are taken up against a concentration gradient Active transport uses energy An NPK fertiliser contains nitrogen (N), phosphorus (P) and

potassium (K)

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Plant Senses and Commercial Uses

Plant Senses Commercial UsesPlants respond to their

surroundings to give them a better chance of survival

Plant responses are called tropisms and are controlled by a hormone

Plants respond to light, gravity and water

Remember: unequal distribution of auxin speeds up growth in shoots and slows down growth in roots

1. Growing Cuttings◦ Rooting powder contains synthetic auxins◦ A cutting is taken from a plant and

dipped in this powder. This stimulates the roots to grow quickly and enables gardeners to grow lots of exact copies of a particular plant

2. Killing Weeds◦ Synthetic auxins are used as selective

weed-killers◦ They only affect the broad-leaved weeds;

narrow-leaved grasses and cereals are not affected

◦ They kill the weed by making the weed grow to quickly

3. Seedless Fruits◦ Synthetic auxins are sprayed on

unpollinated flowers◦ Fruits form without fertilisation and thus

form without pips4. Early Ripening

◦ Plant hormones can also be used to ripen fruit in transport

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Responses to Water and Gravity

Response to Water Response to Gravity A plant’s response to water is

called hydrotropism Roots always grow to a certain

extent towards water, even if it means ignoring the pull of gravity and growing sideways

An uneven amount of moisture will cause more auxin to appear on the side with more water

This inhibits the growth of cells on this side

The root cells on the outside will grow quicker and will bend towards the moisture

A plant’s response to gravity is called geotropism

Even if you plant a seed the wrong way up, the shoot always grows up, away from gravity and the root grows down towards gravity

If a plant is put on its side, auxin gathers on the lower half of the shoot and root

Auxin slows down the growth of root cells, so the root curves downwards

Auxin speeds up the growth of the shoot cells so the shoot curves up

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Response to LightA plant’s response to light is called phototropismPlants need light for photosynthesis and thus grow

towards the lightNormally light shines from above. Auxin is spread

evenly and the shoot grows upwards If light comes from one side, auxin accumulates down

the shaded side. Auxin makes these cells grow fasterThe result is that the shoot bends towards the light

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BIOMASS, FARMING AND DECAY

BiomassPyramid of NumbersPyramid of Biomass

Intensive Farming and Organic FarmingPesticidesFertilisersEutrophication

Decay and Food PreservationRecycling of CarbonRecycling of Nitrogen

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Biomass Energy enters food chains in photosynthesis Plants are producers because they produce food Animals are consumers A pyramid of numbers show the number of organisms

in each link (trophic level) in a food chain A pyramid of biomass shows the mass of living

material in each link (trophic level) in a food chain Energy is transferred along a food chain or food web Some energy is transferred into less useful forms such

as hear or body waste Biomass fuels are wood (by burning), alcohol (by

fermentation) and biogas (from decay) Biomass fuels are renewable, produce less pollution

and are energy self-reliant

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Pyramids of NumbersA pyramid of numbers tells us how

many organisms are involved at each stage in the food chain

At each trophic level the number of organisms get less

However, sometimes a pyramid of numbers doesn’t look like a pyramid at all because it doesn’t take into account the size of the organisms◦E.g. There are many fleas on a single fox

which would make the pyramid ‘top heavy’

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Pyramids of BiomassA biomass pyramid takes into

account the size of an organism at each level unlike the pyramid of numbers

It looks at the mass of the organism

You can take the information from the pyramid of numbers and multiply it by the organism’s mass which will achieve the pyramid shape again

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Intensive and Organic Farming Intensive farming uses pesticides (insecticide and

fungicide) to kill pests and herbicides to kill weeds Intensive farming produces more food but also causes

problems such as pesticides accumulation in food chains Fish farming, glasshouses, hydroponics and battery

farming are all examples of intensive farming Organic farming does not use artificial fertilisers,

herbicides or pesticides Organic farming uses animal manure, crop rotation,

hand-weeding and biological control of pests Intensive farming improves the efficiency of energy

transfer in food chains Hydroponics gives better control of fertilisers and

diseases

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Intensive Farming

Intensive farming can produce more food because it is designed to provide more food for the given land

Many people regard intensive farming of animals as cruel

In order to produce more food from the land, fertilisers and pesticides are needed

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PesticidesPesticides are used to kill insects that

damage cropsThey also kill harmless insects, then

insect-eating birds have a shortage of food

The pesticides can get washed into rivers and lake which can then get into our food chains

This was the case in the 60s when a pesticide, DDT, got into the food chain and threatened populations of animals

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FertilisersPlants need nutrients from the soil to

growArtificial fertilisers are used to replace

the nutrients in the soil because there isn’t enough because of intensive farming

Fertilisers enable farmers to crop more crops in a smaller space.

Less countryside will be lost for farming but eutrophication is caused because of fertilisers

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Eutrophication If too much fertiliser is used and it rains, it goes

into rivers and lakesThe water plants grow quicker as a result of this

and they quickly cover the surface of the waterThere is then more competition for light and

some plants dieMicrobes break down the dead plants and use

the oxygen for respirationThe amount of oxygen in the water is then

reduced and animals die through suffocationUntreated sewage can also cause

eutrophication

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Organic FarmingPeople need to limit their needsIntensive farming produces quality food and

enough to supply people’s needs in Europe but has its problems – alternative is organic farming

Organic farming produces less food per area of land but is kinder to the environment

Organic farming uses manure as a fertiliser and has land for wild plants and animals to flourish.

Biological control of pests are also used where animals eat the pests, it’s not as effective but it isn’t harmful

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Decay and Food Preservation Decomposers such as fungi and bacteria cause decay Decay breaks down sewage and compost Decay is affected by temperature and the amount of

oxygen and water Detritivores are animals that feed on dead and

decaying material Earthworms, maggots and woodlice are Detritivores Saprophytes are plants that live on dead and

decaying material Food can be preserved by stopping or reducing decay Food preservation methods include canning, freezing,

drying and adding salt, sugar or vinegar

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Recycling of Nitrogen and Carbon

When plants and animals die, their chemicals, such as nitrogen and carbon, are recycled

Plants remove carbon fro the air by photosynthesis Respiration and the burning of fossil fuels releases carbon in the

form of carbon dioxide Carbon is recycled through marine shells, limestone and eventual

weathering There is 78% nitrogen in the atmosphere but it is unreactive Plants take in nitrogen as nitrates Dead bodies decay, releasing nitrates Decomposers convert proteins and urea into ammonia Ammonia is converted into nitrates by nitrifying bacteria Some nitrates are converted into nitrogen by denitrifying bacteria Nitrogen-fixing bacteria in the soil and root nodules fix

atmospheric nitrogen (This is further explained on the next few slides...)

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THE CARBON CYCLE

Feeding

Decomposers

Death but no decay

Death and Decay

Photosynthesis

Burning and Combustion

Respiration

The atmosphere

Fossil Fuels

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THE CARBON CYCLE IN DETAIL

In the atmosphere, carbon dioxide is a rare

gas, making up only 0.03% of the atmosphere. The amount should stay

that same because plants absorb the carbon that is

realised.

Plants absorb carbon dioxide during

photosynthesis. They use the carbon to make carbohydrates, proteins

and fats using the Sun for energy.

Animals eat the plants and so they absorb the carbon. However, the animals also respire.

Carbon is realised into the soil because the animals

and plants die and produce waste through

death and decay.

However, sometimes the plants and animals die but do not decay. The heat and pressure then produce fossil fuels over

millions of years.

Bacteria and fungi in the soil break down the dead matter, urine and faeces –

all of which contain carbon. The

decomposers realise carbon dioxide when they

respire.

Fossil fuels are produced, making coal from plants as

well as oil and gas from animals. The fossil fuels

then realise carbon dioxide when they are burnt in

the industry.

All plants, animals and decomposers respire.

Respiration then realises carbon dioxide into the

atmosphere again.

Added Notes:Decomposition

•Decomposers are bacteria and fungi which break down dead material•They help recycle carbon into the atmosphere and recycle nutrients into the soil•Plants use this nutrients dissolved in water during photosynthesis.•Animals eat plants, and both animals and plants die, making the cycle start from the beginning again•Decomposition happens everywhere in nature, in compost heaps and even sewage works•The perfect conditions are:

• Warm• Moist• Plenty of oxygen

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THE NITROGEN CYCLE

Nitrogen into Nitrates• Lightening• Artificial

fertilisers• Nitrogen-fixing

bacteria• Nitrifying

bacteria

Nitrates into Nitrogen• Denitrifying

bacteria• Plants and

dissolved in water

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THE NITROGEN CYCLE

1. Nitrogen is in the air

2. Lightening causes nitrogen oxides by

combining oxygen and nitrogen. Dissolved in

the rain, they are washed into the soil and form nitrates.

3. Nitrogen-fixing bacteria in the soil

convert nitrogen in the air into nitrates.

4. Nitrogen-fixing bacteria are in the

roots of some plants, e.g. Beans. The

bacteria form root nodules which

improves the nitrate content of the soil.

5. Fertilisers generated from the

Haber process can be added to the soil to improve the nitrate

content.

6. Plants take the nitrates and convert them into proteins.

7. Animals eat the plants and the protein

becomes part of the animals’ proteins.

8. Animals and plants produce waste.

9. Animals and plants die and their bodies

decay.

10. Detritivores, e.g. worms, feed on the decaying material

which make it easier for decomposers to break

down.

11. Decomposers, e.g. Bacteria, turn this

material into ammonium

compounds – which contain nitrogen.

12. Nitrifying bacteria in the soil

change ammonia into nitrates.

13. Nitrates can be washed out of the soil before they are used.

This is called leaching and can have serious

consequences for rivers and streams.

14. Denitrifying bacteria live in

waterlogged soils and change nitrates back into ammonia which returns nitrogen into

that atmosphere again

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THE NITROGEN CYCLEADDED NOTES•The atmosphere contains 78% nitrogen gas•Nitrogen is needed to make protein•Plants and animals cannot use nitrogen as a gas – it has to be converted into nitrates•Animals get protein by eating plants which plants make from nitrates•It is a continuous cycle•There are four ways that nitrogen is converted into nitrates and only two ways that nitrogen is taken out of the soil•There are three different types of bacteria involved in this cycle:

• Nitrifying bacteria• Nitrogen-fixing bacteria• Denitrifying bacteria

Nitrates

Nitrogen in the air

Soil

Death and DecayProteins in

AnimalsFertilisers

Proteins in Plants

1

12

7 11

89

14

10

13

6

5

43

2

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Key/ Scientific Words

The Carbon Cycle The Nitrogen Cycle

PhotosynthesisRespirationCombustionCarbonFossil fuelsDecomposers/

decompositionNutrientsWarmthMoistureOxygen

LighteningNitratesNitrogenNitrogen-fixing bacteriaRoot nodulesProteinDetritivoresDecomposersNitrifying bacteriaLeachingDenitrifying bacteria

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More Key/ Scientific Words... Xylem

Phloem Transpiration Starch Vascular bundle Nitrates Phosphates Potassium Magnesium Iron Osmosis Large surface area Transpiration stream Cuticle Stomata Guard cells Light Temperature Humidity Flaccid Turgid Carbon dioxide

Water Glucose Oxygen Photosynthesis Cellulose Lipids Proteins Enzymes Epidermis Palisade cells Leaf vein Spongy layer/

mesophyll Chloroplasts Chlorophyll Active transport Diffusion Semi-permeable Net movement Plasmolysis Haemolysis Limiting factors

Lignin Concentration gradient Biomass Pyramid of numbers Trophic level Biogas Fermentation Pesticides Intensive farming Organic farming Fertilisers Eutrophication Hydroponics Decomposers Detritivores Saprophytes Tropisms Auxin Hydrotropism Geotropism Phototropism

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