GCSE Biology B5

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Monoclonal Antibodies

Monoclonal antibodies are identical copies of antibodies made in labs. They have many uses, like pregnancy tests, diagnosing cancer and treating it.

However, they need to be in large numbers to work.

Hybridoma cells are two types of cells fused together. There are three stages to making a hybridoma cell, which are-

  • A particular antigen is injected into a mouse. The mouse produces lymphocytes ( B and T cells) that make antibodies against the antigen. 
  • There are cancer cells growing in a medium. The B cells are taken out from the mouse and the two are fused.
  • This creates a cell that can produce antibodies and divide quickly. These are hybridoma cells.
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Antibiotics and Developing New Medicines

There are many phases to creating a new medicine.

  • Identifying the pathogen and how it affects cells (using cell tissue culture).
  • Animal testing-finding specific amounts and side effects. - A Few Years
  • Then tested on 20-100 healthy humans. - A Few Months
  • Tested on people with the disease. Only 20% of phase 1 drugs make it to phase 2. Up to two years.
  • Phase 3 tests on more people, only 33% of drugs from phase 2 reach phase 3.
  • Phase 4 is the final stage, where the drug has to be approved by FDA. They discuss its cost-effectiveness and dosage.
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Plants-Disease Transmissions & Defence

Plants can transmit diseases directly or indirctly (soil, seeds, machinery.). Fungi produce spores in wind and water and animal vectors (elm bark, birds, aphids, humans, etc..). 

Factors affecting transmission-

  • Choice of plant type and overcrowding
  • Poor mineral availability (reduces health in general). Poor control of imports and exports.
  • Damp, warm  conditions
  • Climate change

Physical barriers include waxy cuticle on leaves, bark on trees, cellulose cell walls, lignified cell walls and callus formation.

Physical defence is a rapid, unspecific response. Callose synthesised and deposited between cell wall and membrane and the plasmodesmata.There is also thickening an depositing of lignin. Callose blocks the sieve plates in the pholem, sealing off infected cells.

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Photosynthesis

Equation = Carbon Dioxide + Water = Oxygen + Glucose (+energy  (ATP))

Photosynthesis is an endothermic reaction.

Plants can only produce biomass in the day. At night, they respirate. Respiration is the photosynthesis equation 'flipped'.

  • Glucose links together to make starch. This is becaue glucose left alone would dissolve in water.
  • This stays in the chloroplasts until photosynthesis stops.
  • Starch is broken dwn into simpler substances and then moved around/into the cytoplasm.
  • It is used to make sucrose. This is transported around the plant and can be ued to make-

Starch, which is found in a storage organ, Cellulose, lipids or proteins and glucose.

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Adaptations for Photosynthesis

Leaves are adapted for photosynthesis - 

  • Big and thin to absorb maximum amounts of sunlight
  • Large surface area
  • Palisade cells contain chloroplasts and chlorophyll that absorbs sunlight.
  • Tiny holes on the underside of the leaf for gas exchange.
  • Stomata allow carbon dioxide into leaves and water and oxygen can escape.
  • Thin/short diffusion distance so the process is faster.

Light Intensity = 

Limiting factors are light, temperature and carbon dioxide levels.

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Absorbing Water and Mineral Ions

Diffusion - Particles move from a high to a low concentration gradient.

Osmosis - Water moves from a high concentration to a low concentration through a partially permeable membrane.

Active transport - Energy is used to move particles from a low to a high concentration. This uses a carrier protein.

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Transport in Plants & Transpiration

Xylem vessels are dead. They form tiny vessels leading from a plant's roots up to its leaves. Inside the vessels is an unbroken chain of water, due to the weak attraction force between the water molecules.

Water is pulled up xylem vessels in the stem as water evaporates from the leaves. As the water vapour diffuses, more water evaporates from the xylem inside the leaf.

Transpiration - 

The evaporation of water from leaves keeps them cool and helps water (and dissolved mineral ions) up the plant. The flow of water into a root up the stem and out of the leaves is called transpiration.

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Xylem & Phloem Vessels

Xylem Vessels (Dead)-

  • Carry water and dissolved mineral ions.
  • Thick side walls and rings of lingnin form rigid tubes-provide support, will not burst.
  • No cytoplasm, more room for water to flow through.
  • Lack of cell walls between cells means that water flow is not slowed down.
  • Tiny pores allow water and mineral ions to enter and leave xylem vessels.

Phloem Vessels (Alive)-

  • Holes in the end of the cell walls allow liquids to flow from one sieve cell to another.
  • Sucrose solution can be pumped through pores.
  • Sieve cells & Companion cells
  • Small amount of cytoplasm and no nucleus mean there is more room fro the central channel.
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Plant Hormones

Plants respond to stimuli to-

  • Avoid stress
  • Avoid being eaten
  • Enhance survival and chances of having offspring

The way a plant grows is controlled by hormones. They are sensitive to the environment and can make adjustments to help survival. 

Gibberellin- 

  • Seed germination
  • Stem growth
  • Flowering
  • Promotes cell dvision and elongation (lengthening the stem)
  • If a dwarf variety of plant is sprayed with gibberellin, it will grow to the same height as normal plants of that species.
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Plant Hormones 2

Cytokinins- 

  • Promotes cell division.
  • Found in actively growing plant cells and developing fruit and seeds.
  • Mainly grow at root tips, shoot tips and leaves.

Ethylene- 

  • Used to ripen fruit.
  • Makes it easier to transport as plnts can be picked unripened and sprayed with ethylene at its destination.

Abscisic Acid- 

  • Slows down/stops growth by slowing down metabollism.
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Tropisms

Tropism is how plants respond to their environment.

Phototropism's stimulus is light. Plants grow towards the stimulus (light).

Geotropism's stimulus is gravity. The plant grows away from the ground (gravity).

Chemotropism's stimulus is chemicals. The plant's roots grow towards chemicals in the ground.

Thigmotropism's stimulus is triggered by sensing other plants of a fly in a venus fly trap. The plant closes the trap or winds round the other plant nearby.

Hydrotropism's stimulus is water. The roots grow towards water.

When plants grow towards light, it is positively phototropic. Root growth away from light could be seen as negtively phototropic but gravity dictates their growth directioin.

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Auxin

Plant stems always grow towards the light. This growth is controlled by auxin. If plants recieve light from one side, they will grow towards it. The auxin is produced at the tip of the new shoot. It makes the cells bend/elongate more on the shaded side so it bends towards the light.

Direct sunlight breaks down auxin. This means that the side of the shoot with most direct sunlight will have the least amounts of auxin and the shadiest side will have most amount of auxin. This means there will be more growth on the shaded side.

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Uses of Plant Hormones

Weed Killers- 

  • Artificial auxins make a plant grow uncontrollably, killing it.
  • Selective weedkillers contain artificial auxins to kill plants with broad leaves (dandelions, chickweed) but not those with narrow leaves (wheat,grass)
  • Farmers can therefore kill weeds without killing their own crop.

Rooting Powders- 

  • Powder contains auxins.
  • Cuttings are dipped in powder.
  • Promotes root growth.

Fruit Ripening- 

  • Ethene promotes fruit ripening- converts starch into sugar.
  • Naturally given off by ripe fruits
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Uses of Plant Hormones 2

Gibberellins- 

  • Released inside a seed to start germination.
  • Some seeds need a period of darkness or cold before they can start germination. Gibberellin can start germination without this.

Photoperiodism-

  • The resopnse in an organism to the amount of daylight hours. They might use this to flower at a certain time.
  • Flower growers can override this by spraying the flowers with gibberellin.
  • Many plants only produce seeds after being pollinated , which allows egg cellls to be fertilised and seeds to form.
  • Gibberellins can cause plants to produce fruit without this, giving us seedless fruit.
  • Gibberellins can cause some fruit to be produced bigger.
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