B4: The processes of life

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Why are there chemical reactions in cells?

  • All living things carry out 7 life processes:








  • All of these processes depend on chemical reactions in cells and many reactions need energy.
  • This energy is released by the 7th life process: Respiration.
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What are enzymes?

  • Enzymes- Speed up chemical reactions in cells;natural catalyst.
  • They are proteins.
  • Genes carry instructions to make them.
  • Reacting molecules must fit exactly into the active site of the enzyme.
  • Every enzyme has its own shape; the Lock and Key model.
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What conditions do enzymes need?

  • They work best at their optimum temperature (high rate of reaction)
  • Below this temp, they are slow.
  • If the temp is too high, enzymes change shape, it no longer catalyses its reaction - It has been Denature.

Its activity is a balance between:

  • Increasing reaction rate as temp increases.
  • Changes to the active site as temp increases above the optimum.

Also work best at their optimum PH. Other PH values change its active site's shape; the protein they break down no longer fits.

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What is photosynthesis?

  • Photosynthesis- plants use sunlight to make their food.

The process:

  • Chlorophyll, green pigment, absorbs light energy.
  • Energy allow reactions - Carbon dioxide and water become glucose and water; oxygen = waste product.

Photosynthesis also happens in microorganisms such as phytoplankton.

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What happens to the glucose?

  • It is made during Photosynthesis.

3 main uses:

  • Made into chemicals plant cells need to grow; Chlorophyll, Proteins & Cellulose.
  • Join together to make starch molecules; storage chemical.
  • Used in Respiration.
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What's in a plant cell?

Parts of a plant cell and their function:

  • Chloroplasts- contain Chlorophyll and enzymes for Photosynthesis.
  • Nucleus- Contains DNA; code for making enzymes and other proteins for Photosynthesis.
  • Cytoplasm- Enzymes and other Proteins are made.
  • Cell membrane- Controls the diffusion of chemicals, gas and water, in and out of the cell; prevents bigger molecules escaping (Glucose).
  • Mitochondria- Where Respiration occurs.
  • Vacuole- Contains Glucose molecules, dissolved in water.
  • Cell wall- Rigid; made of cellulose.
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How do chemicals get into cells?

  • Molecules get in and out of cells by Diffusion.
  • Diffusion- Movement of molecules from region of high concentration to one of low; Passive process (needs no extra energy).
  • Carbon dioxide diffuses into leaves, Oxygen diffuses out of leaves.
  • Water enters through a Partially-permeable membrane.
  • Water diffuses through Osmosis.
  • Osmosis- Movement of Water from a dilute solution to a more concentrated one.
  • Minerals enter plants through root cells.
  • Active Transport- moves nitrate ions across cell membrane. Energy from Respiration moves the particles from a region of high concentration to lower concentration.
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What speeds up Photosynthesis?

Factors the affect the rate of Photosynthesis:

  • Temperature- Faster at higher temperatures.
  • Carbon Dioxide concentration- Increasing this speeds up Photosynthesis.
  • Light Intensity- Increasing the amount of light, increases the rate of Photosynthesis; up to a certain point.
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How can we investigate Plants and Light?

Different plants are adapted to different light levels. You can investigate this by using:

  • Light Metre- Measure light intensity.
  • Quadrat(placed at random) and Identification key- Survey plants in sq metre.
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Why do living organisms need energy?

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What is aerobic respiration?

  • Aerobic respiration releases energy.
  • It happens in plants and animal cells and in some microorganisms; it needs oxygen.
  • Glucose (C6H12O6) + Oxygen (6O2) = Carbon Dioxide (6CO2) + Water (6H2O)
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What is Anaerobic Respiration?

  • Anaerobic Respiration releases less energy than Aerobic respiration.
  • It happens in plants and animals cells and in some microorgansims when there is little or no Oxygen:

-In plant roots when the soil is waterlogged.

-In human muscle cells during vigorous exercise.

  • Anaerobic respiration in animal cells and some bacteria:

Glucose = Lactic acid

  • Microorganisms such as yeast:

Glucose = Ethanol + Carbon Dioxide 

  • Anaerobic respiration of yeast produces carbon dioxide which makes bread rise and ethanol for alcoholic drinks.
  • Some bacteria produce methane gas which is a useful fuel.
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What's in a cell?

Animal cell

  • Cell Membrane- Allows gases and water to pass freely in and out of the cell, controls passage of other molecules.
  • Cytoplasm- Where enzymes are made. Where anaerobic reapiration takes place.
  • Mitochondria- Contains enzymes for aerobic respiration.
  • Nucleus- Holds genetic info for enzymes involved in respiration.

Bacteria cell

  • Cell wall
  • Cell membrane- Allows water and gases to pass freely and forms a barrier for other chemicals.
  • Cytoplasm- Where enzymes are made,location of respiration reactions.
  • Strand of circular DNA- Holds genetic info for enzymes involved in respiration.

Yeast cell

  • Same as animal cell but with a Cell wall.
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