Additional Science - B4

Few notes on Biology section - missing Nitrogen and Carbon cycle though!


Leaf Structure

First of all...
Carbon dioxide + water -> glucose + oxygen 

Leaves are designed for making food and photosynthesis:
the leaf structure clockwise - waxy cuticle, upper epidermis, chloroplast, vein, lower epidermis, waxy cuticle, guard cell, stoma, air space, spongy mesophyll layer, palisade mesophyll layer. 

Important features of leaves

  • Leaves are broad = large surface area for light
  • Leaves are thin = Co2 and water vapour have a short distance to reach photosynthesizing cells
  • Air spaces in spongy layer = gases like Co2 and O2 to move easily
  • Lots of chlorophyll = absorbs light energy
  • Upper epidermis is transparent = light can pass through palisade layer
  • Lower surface full of stoma = gases (Co2 & O2) in and out plus water to escape (transpiration)
  • Network of veins = deliver nutrients and help support the leaf structure
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Leaf Structure - part 2

Leaf Palisade Cells are designed for photosynthesis

What is a palisade cell? They make sugars by photosynthesis.  They contain a lot of chloroplasts to absorb light.

What is the structure of a palisade cell?  They have a tall shape, which means they have a lot of surface area for absorbing Co2.

What else are they used for?  Tall shape = more chance of light hitting a chloroplast.

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Diffusion in Leaves

Diffusion is totally RANDOM and happens ALL BY ITSELF

The definition of diffusion:  Diffusion is the passive movement of particles from an area of higher concentration to an area of lower concentration

Plants exchange gases by diffusion:  
Photosynthesis = use up Co2, produce O2;
Respiration = use up O2, produce Co2. 

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Osmosis is a special case of diffusion:
The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration

What is a partially permeable membrane?
A membrane which allows only tiny molecules (like water) to pass through. 

Turgor pressure supports plant tissues

  • When a plant is well watered, the cell will draw water in by osmosis and become plump and swollen = known as turgid.
  • The contents of the cell push against the cell wall = known as turgor pressure. 
  • If there's no water in the soil, the plant will wilt = water lost, turgor pressure lost. The cell is now known to be flaccid.
  • If the plant is really short of water, the cytoplasm inside the cell starts to shrink and the membrane pulls away from the cell wall = cell is plasmolysed. The plant doesn't lose its shape though, the inelastic cell wall keeps things in position.
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Water flow through plants

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Water flow through the plants - part 2

Transpiration is the loss of water from the plant

  • Transpiration is caused by the evaporation and diffusion of water from inside the leaves - this creates a slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through xylem vessels.
  • There is a constant transpiration stream of water through the plant.
  • Gases can be exchanged easily due to stomata in them.

Water creates turgor pressure in the plant cells = stops the plant from wilting! 

Water enters through the roots; water evaporates from the leaves.

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Water flow through plants - part 3

Transpiration rate is affected by four main things:

  • LIGHT INTENSITY - the brighter the light, the greater the transpiration rate.
  • TEMPERATURE - the warmer it is, the faster transpiration happens.
  • AIR MOVEMENT - if there's lots of air movement around the leaf, transpiration happens faster.
  • AIR HUMIDITY - if the air around the leaf is very dry, transpiration happens more quickly. 

Plants need to balance water loss with water uptake

  • Plants have adaptions to help reduce water loss from their leaves:
    - Leaves usually have a waxy cuticle covering the upper epidermis - this makes the upper surface waterproof.
    - Most stomata are on the lower surface of the leaf = slows downs diffusion.
    - The bigger the stomata, the more water the plant will lose.  Plants in hot climate conserve water so they have fewer stomata. 
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Water flow through plants - part 4

Stomata open and close automatically

  • Stomata close automatically when supplies of water from the roots start to dry up. 
  • The guard cells have a special kidney-like shape which opens and closes the stomata as the guard cells go flaccid or turgid.
  • Thin outer walls are thickened inner walls make this opening and closing function work properly.
  • Open stomata allows gases in and out for photosynthesis. 
  • Sensitive at night so they close up - allowing to conserve water without losing out on photosynthesis.
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Transport system in plants

Humans have one circulatory system, plants have two: xylem and phloem.

Phloem tubes transports food:

  • Made of coloumns of living cells with perforated end-plates for stuff to flow through.
  • They transport food substances - mainly sugar.
  • Movement of food substances around the plant is known as translocation.

Xylem tubes take water up:

  • Made of dead cells joined end to end with no end walls between them and hole down the middle.
  • The thick side walls are strong and stiff, which gives the plant support.
  • They carry water and minerals from the roots up to the shoot of the leaves in the transpiration stream.

You can recognise xylem and phloem by where they are - they usually run alongside each other in vascular bundles (like veins).

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Minerals needed for healthy growth

Plants need three main minerals:

  • Nitrates - contain nitrogen to make amino acids and proteins.  Needed for cell growth.  If no nitrate, plant will be stunted with yellow leaves.
  • Phosphates - contain phosphorus for making DNA and cell membranes.  Needed for respiration and growth.  If no phosphates, plants will have poor root growth and purple leaves.
  • Potassium - to help enzymes.  Needed for photosynthesis and respiration. If no potassium, plants have poor flower and fruit growth with discoloured leaves.

Magnesium is also needed in small amounts.  It is required for making chlorophyll.

Root hairs take in minerals using active transport:
Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient - and therefore require an input ofenergy from the cell. 

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Pyramids of numbers and biomass

You need to construct pyramids of number

Each bar on a pyramid of numbers shows the number of organisms at that stage of the food chain, e.g.:

  • 5000 dandelions... feed... 100 rabbits... which feed... 1 fox.

The 'dandelions' bar will be much longer than the 'rabbits' bar, which should then be longer than the 'fox' bar.  Dandelions go at the bottom as they are the bottom of the food chain.

This gives a typical pyramid of numbers, where the higher you go up the pyramid, the number of organisms go down - it takes a lot of food from the level below to keep one animal alive.

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Pyramids of number and biomass - part 2

You need to construct pyramids of biomass

Each bar on a pyramid of biomass shows the mass of living material at the stage of the food chain - basically how much all the organisms weigh if you put them all together.

So... one pear tree would have a big biomass and the hundreds of fleas would have a very small biomass.

Biomass pyramids are pratically always the right shape!

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Energy transfer and energy flow

Energy from the Sun is the source of energy for nearly all life on Earth:

  • Plants use a small percentage of the energy from the Sun to make food during photosynthesis.  This energy works its way through the food web as animals eat plants.
  • The energy lost at each stage is used for staying alive (respiration). 
  • Most of this energy is eventually lost to the surroundings as heat.
  • Material and energy are also lost from the food chain in the droppings - egestion.

You need to interpret data on energy flow -
Rose bush - 80 000 kJ; greenfly - 10 000 kJ; ladybird - 900 kJ; bird - 40 kJ.

  • The numbers show the amount of energy available to the next level.
  • You can work out how much energy has been lost at each level by taking away the energy available to the next level. e.g. 80000 kJ - 10000 kJ = 70000 kJ lost.
  • Efficiency = energy available to the next level / energy that was available to the previous level x 100
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Biomass & intensive farming

Energy stored in biomass can be used for other things:

  • You can eat it, feed it into live stock, grow the seeds of plants and use it as fuel.

You can also use biomass for fuel:

  • Fast-growing trees - cutting down trees is not a bad thing if they are replaced with fast-growing and planted especially for that purpose.  Replacement trees are still removing Co2 from the atmosphere.
  • Fermenting biomass using bacteria or yeast - breaking down by anaerobic respiration.  Micro-organisms from plant and animal waste in a simple fermenter called a digester, the biogas can be burned to release energy.

Using biofuels reduces air pollution! No acid rain gases are produced when wood and biogas burn.

Did you know - theoretically, you can supply all your energy from household waste.

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Biomass & intensive farming - part 2

Intensive farming is used to produced more food:
Farmers can do this is different ways, but they all involve reducing the energy losses that happen at each stage in a good chain, e.g. -

  • Herbicides to kill weeds - more energy from the sun falling on their crops.
  • Pesticides to kill insects that eat crops - no energy is transferred into a different food chain.
  • Battery farmed animals - kept close together indoors in small pens, so they're warm and can't move about.  This saves them wasting energy as they move around.

Intensive farming allows us to produce a lot of food with less land.

Intensive farming can destroy the environment:
Intensive farming methods are efficient, but they raise ethical dilemmas because they damage the world we live in by - carelessness use of fertilisers can pollute lakes/rivers; pesticides disturb food chains; intensive farming on animals is cruel and removal of hedges destroys wild habitats. 

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Pesticides and biological control

Pesticides disturb food chains

  • Pesticides are sprayed on crops to kill the creatures that damage them, but they also kill harmless insects such as bees and beetles.
  • This can cause a shortage of food for animals further up the food chain.
  • Pesticides also tend to be toxic to creates that aren't pests and there's danger of the poison passing on through the food chain. Even a risk for humans. 

You can use biological control instead of pesticides

  • Biological control means using living things instead of chemicals to control a pest.  E.g. a predator, a parasite or a disease to kill the pest.
  • Aphids - they eat roses and vegetables.  Ladybirds are aphid predators, so people put them into their fields to keep the number of aphids down.
  • Wasps and flies produce larvae which develop on or in a host insect, which eventually kills the insect host.
  • Myxomatosis is a disease which kills rabbits - this was used in Austrailia when the rabbit population grew.
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Biological control

Advantages of biological control:

  • The predator, parasite or disease usually only affects the pest animal.
  • No chemicals are used so there's less pollution, disruption of food chains and risk of people eating the food that's been sprayed.

Disadvantages of biological control:

  • It's slower than pesticides - you have to wait for your control organism to build up its numbers.
  • Biological control won't kill all the pests, and it usually only kills one type of pest.
  • It takes more management and planning, workers also need training and educating.
  • Control organisms can drive out native species or become pests in their own right.
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Alternatives to intensive farming

Hydroponics is where plants are grown without soil
Most commercially grown tomatoes and cucumbers are grown in nutrient solutions instead of in soil.

Advantages of hydroponics:

  • Takes up less space so less lang required.
  • No soil preparation or weeding needed.
  • Many pests live in soil, so it avoids these.
  • Mineral levels can be controlled more accurately.

Disadvantages of hydroponics:

  • It can be expensive to set up and run.
  • Need to use specially formulated soluble nutrients.
  • Growers need to be skilled and properly trained.
  • There's no soil to anchor the roots to support the plant.
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Alternatives to intensive farming

Organic farming is still perfectly viable
1) The use of organic fertilisers (animal manure) recycles nutrients.  It doesn't work as well as artificial fertilisers, but it is better for the environment. 
2) Crop rotation - growing a cycle of different crops in a field each year.  This stops the pests and diseases of one crop building up, and stops nutrients running out.
3) Weeding - physically removing weeds, no nasty chemicals involved.
4) Varying seed planting times - sowing seeds later/earlir in the season to avoid major pests on that crop. 

Advantages/disadvantages of organic farming:

  • Organic farming takes up more space than intensive farming.
  • It's more labour-sensitive - more jobs, expensive goods.
  • You can't grow as much food.
  • Organic farming uses fewer chemicals.
  • Better for the environment.
  • Organic farming = no battery farming. 
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Things decay because of micro-organisms

  • Living things are made of materials they take from the world around them.
  • When they die or decompose, elements are returned to the soil/air.
  • These elements are then used by plants and the cycle repeats.
  • Nearly all decomposition is done by soil bacteria or fungi.
  • Important elements (carbon, hydrogen, nitrogen, oxygen) are recycled.
  • The rate of decay depends on three main things: temperature; moisture and oxygen.  These factors cause decomposers to grow and reproduce more quickly.

Food preservation methods reduce the rate of decay:

  • Canning
  • Cooling
  • Freezing
  • Drying
  • Adding salt/vinegar
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