Biology B4

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Cell structure and function of animal cells

Animal cell: 1) Nucleus - contains DNA. This contains instructions for making proteins, eg. enzymes

2) Cytoplasm - gel like substance where proteins like enzymes are made. Some enzyme controlled reactions take place in the cytoplasm eg. the reactions of anerobic respiration and photosynthesis. .

3) Cell membrane - holds the cell together and controls what goes in and  out. It lets gases and water pass through freely while acting as a barrier to other chemicals.

4) Mitchondria - these are where the enzymes needed for the reactions of areobic respiration are found, and where the reactions take place.

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Cell structure and function of plant cells

Plant cells have a few extra things that animal cells don't have:

1) Rigid cell wall - made of cellulose. It supports the cell and strengthens it.

2) Vacuole - contains cell sap, a weak solution of sugar and salts.

3) Chloroplasts - these are where the reactions for photosynthesis take place. They contain a green substance called chlorophyll and the enzymes needed for photosynthesis.

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Yeast

Yeast are single celled microorganisms

1) Yeast are used to make bread and wine 

2) These are the different parts of a yeast cell:

Cell membrane

Cytoplasm

Nucleus

Mitochondria

Cell wall

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Bacteria

Bacteria have a simple cell structure:

1) Bacterial cells are a bit different to plant, animal and yeast cells. You need to know the different parts fo a bacterial cell:

Cell membrane

Cell wall

Cytoplasm

Circular DNA molecule

2) The don't have a nucleus. They have a circular molecule of DNA which floats around in the cytoplasm.

3) They don't have mitochondria either, but they can still respire aerobically.

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Enzymes

Enzymes are proteins produced by living things

Living things produce thousands of different chemical reactions going on inside them all the time. These reactions need to be carefully controlled -- to get the right amount of substances. So.... living things produce enzymes:

ENZYMES are proteins that SPEED UP CHEMICAL REACTIONS

Enzymes are very specific:

Chemical reactions usually involve things either being split apart or joined together. A substrate is a molecule that is changed in a chemical reaction. Every enzyme molecule has an active site -- the part where a substrate joins on to the enzyme. Enzymes are really picky -- they usually only speed up one reaction. This is because for an enzyme to work, a substrate has to be the correct shape to fit into the active site. This is called the 'lock and key' model, because the substrate fits into the enzyme like a key fits into a lock.

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Enzymes need the right temperature and pH

Enzymes need to be at a specific constance temperature to work at their optium (when they're most active). 

1) Changing the temperature changes the rate of an ezyme-controlled reaction.

2) A higher temperature increases the rate at first.

3) But, if it gets too hot, some of the bonds holding the enzyme together break. This changes the shape of the enzymes active site and so the substrate will no longer fit and the enzyme won't work any more. It is said to be denatured.

4) All enzymes also have an optium pH that they work best at.

5) If the pH is too high or too low, it interferes with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme.

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Respiration

Respiration is NOT "breathing in and out".

Respiration is a series of chemcial reactions that release energy by breaking down large food molecules. It happens in every living cell.The energy released by respiration is used to power some of the chemcial reactions that happens in cells e.g. the reactions involved in:

MOVEMENT - Energy is released to make muscles contract.

ACTIVE TRANSPORT - This process uses energy to move some substances in and out of cells 

SYNTHESIS OF LARGE MOLECULES - Lots of large molecules (polymers) are made by joining smaller molecules together - this requires energy. For example:

Gluclose is joined together to make things like starch and celluolse in plant cells.

In plant cells, animal cells and microorganisms, glucose and nitrogen are joined together to make amino acids. The animo acids are joines together to make proteins.

There are two types of respiration - aerobic and anaerobic

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Aerobic respiration

Aerobic respiration needs plenty of oxygen

1) Aerobic just means with oxygen

2) It releases more energy per glucose molecule than anaerobic respiration.

3) This is the the type of respiration that you're using most of the time.

4) Aerobic respiration takes place in animal and plant cells, and in some microorganisms.

Word equation:

Glucose + oxygen ----> Carbond fioxide + water ( +Energy released)

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Anaerobic respiration

Anaerobic respiration doesn't use oxygen

1) Anaerobic just means without oxygen

2) Anaerobic respiration takes place in animal and plant cells and some microorganisms when there's very little or no oxygen. For example:

HUMAN CELLS - When you do really vigorous exercise your body can't supply enough oxygen to your muscle cells for aerobic respiration - they have to start respiring anaerobically.

PLANT CELLS - If the soil a plant's growing in becomes waterlogged there'll be no oxygen avaliable for the roots -- so the root cells will have to respire anaerobically. 

BACTERIAL CELLS - Bacteria can get under your skin thorugh puncture wounds caused by things like nails. There's very little oxygen under your skin, so only bacteria that can respire anaerobically can survive there.

Energy is always released during anaerobic respiration, but the products of the reactions are different depending on the type of cell it happens in.

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Anaerobic respiration

Anaerobic respiration can produce lactic acid

In animal cells and some bacteria anaerobic respiration produces lactic acid:

Glucose ---> Lactic acid (+Energy released)

Anaerobic respiration can also produce ethanol and carbon dioxide.

1) In plant cells and some microorganisms (like yeast), anaerobic respiration produces ethanol and carbon dioxide:

Glucose ---> Ethanol + carbon dioxide (+Energy released) 

2) Fermentation is when microorganisms break down sugars into the other products as they respire anaerobically. Humans use fermentation to make lots of things, for example:

  • BIOGAS - This is a fuel used for things like heating and lighting.
  • BREAD - Is made using yeast.
  • ALCOHOL - Yeast ferment sugar to form alchohol (ethanol)
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Photosynthesis

Photosynthesis produces glucose

PHOTOSYNTHESIS is a series of chemical reactions that USES ENERGY from SUNLIGHT to PRODUCE FOOD.

The 'food' it produces is glucose - a sugar. Photosynthesis happens in:

  • The cells in green parts of plants eg. leaf cells
  • Some microogranisms e.g. phytoplankton

Chlorophyll is needed for photosynthesis to happen. It's a green substance which absorbs sunlight and allows energy to be used to convert carbon dioxide (CO2) and water into glucose

Oxygen is produces as a waste product of photosynthesis:

Carbon dioxide + water ---> glucose + oxygen

Organisms that photosynthesise form the start of food chains. They make the energy from the sun avaliable to other organisms by converting it to glucose. The energy is transferred when the photosynthesis organisms are eaten.

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Glucose

  • Plants use glucose in three main ways 

1) Glucose is used for respiration 

  • Plants use some of the glucose for respiration
  • Thid process releases energy from the glucose

2) Glucose is used to make chemcials for growth

  • Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant.
  • Glucose is combined with nitrogen (from nitrates taken up from the soil by plant roots) to make amino acids, which are the made into proteins.
  • Glucose is also used to help make chlorophyll.

3) Glucose is stored as starch

  • Glucose is turned into starch and stored in roots, stems and leaves. It's used at times when the rate of photosynthesis is slower, like in the winter.
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Rate of photosynthesis

Three factors affect the rate of photosynthesis 

1) There are three factors that can affect the rate of photosynthesis .....

  • Amount of light 
  • Amount of CO2
  • Temperature

2) Any of these three factors can become the limiting factor. This just means that it stops photosynthesis from happening any faster.

3) Which factor is limiting at a particular time depends on the environmental conditions:

  • at night it's pretty obvious that light is a limting factor
  • in winter it's often the temperature
  • if it's warm enough and bright enough, the amount of CO2 is usually limiting

  1) Not enough light slows down the rate of photosynthesis                       2) Too little carbon dioxide also slows it down            3) The temperature has to be just right

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Investigating photosynthesis

Investigating the affect of light on plants.

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Investigating photosynthesis

Investigating the affect of light on plants.

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