AQA Biology 2

AQA Biology 2

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  • Created by: kieron
  • Created on: 20-05-10 14:03

Life and Cells

Animals- Nucleus, cytoplasm, cell membrane, mitochondria and ribosomes

Plants- (As animals but..) Rigid cell wall, permanent vacuole, chloroplasts

Cells make tissues, tissues make organs, organs make systems.

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Specialised Cells

Palisade Leaf Cells- Lots of chloroplasts for photosynthesis and tall shape for getting CO2

Guard Cells- Open and close to let gases in or stop them getting out.

Red blood cells- Concave shape and no nucleus so a big surface area for haemoglobin

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Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration

Happens in liquids and gases

The rate of diffusion depends on distane, concentration difference and surface area

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Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration.

A partially permeable membrane is one with very small holes in it

Water moves in and out of cells by osmosis so there's the right concentration

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Carbon dioxide + water ------------> glucose + oxygen

The arrow is Sunlight and chlorophyll

Photosynthesis produces glucose which is food for plants

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The Rate of Photosynthesis

If there's not enough light the rate of photosynthesis will be slow so you need more light intensity

Too little carbon dioxide slows down the rate

And the temperature needs to be just right because at 45 oC the enzymes are destroyed.

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How Plants use glucose

For respiration

Making fruits

Making cell walls

Making proteins

Stored in seeds

Stored as starch

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Minerals for healthy growth

Nitrates make amino acids and deficiency shows stunted growth

Magnesium makes chlorophyll and deficiency shows yellow leaves

Monoculture is where one crop is always grown in the same field and the plant all need the same nutrients

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Pyramids of Number and Biomass

Each feeding level is called a "Trophic level"

Each bar shows how much all the organisms at that level weigh together

Biomass decreases as you go up

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Energy Transfer and Decay

Nearly all energy comes from the Sun

Material and energy are lost in each stage through respiration (like movement) and inedible materials (like bone).

Decay cycles elements back to the start of the food chain for new plants to use, they are broken down by microorganisms (which work best in warm moist conditions with lots of oxygen), they use the waste products that had been made into complex compounds by plants.

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Managing Food Production

To improve the efficiency of food production you can reduce the number of stages in the food chain and restrict the energy lost by farm animals.

^This makes it cheaper

It makes conflict that the animal conditions are cruel and it encourages the spread of disease.

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The Carbon Cycle

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Biological Catalysts- Enzymes

A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction.

Each enzyme has a unique shape which "fits" a substance, usually only 1 type

They need the right temperature and pH or they will denature, in the human body usually 37 oC.

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Enzymes and Respiration

Respiration is the process of releasing energy from glucose, which goes on in every cell.

Aerobic respiration: Glucose +oxygen --> carbon dioxide + water + Energy

Respiration releases energy for building larger molecules from smaller ones and letting muscles contract for movement.

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Enzymes and digestion

Digestive enzymes break big molecules down into smaller ones

Amylase (made in the salivary glands) turns Starch into Simple Sugars

Protease (stomach) turns Proteins into Amino Acids

Lipase converts Fats into Glycerol and Fatty Acids

(All these are made in the pancreas and small intestine as well)

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The Digestive System

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Uses of enzymes

Used in detergents and washing powders to digest things like proteins and fats.

Used to change foods, pre-digest food for babys

In industry, good as they need low temperatures and pressures so less cost and energy, bad as they need to be tightly controlled (can be denatured by a small change in temperature or pH).

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Homeostasis is the maintenance of a constant internal environment.

Things need to be controlled:- Body temperature - Water content - Ion content - Blood sugar level - Carbon dioxide (get rid of) - Urea (get rid of)

When too hot: hairs flat, sweat produced which evaporates, blood vessels on skin dilate

Too cold: hairs stand up, no sweat, skin blood vessels cut off their supply

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The Kidneys and Homeostasis

Remove Urea- when excess amino acids turned into fats and carbohydrates, urea is a waste product and is poisonous, kidneys put it in urine

Adjust Ion Content- If wrong too much or too little water in cells by osmosis, excess ions removed by kidneys and sweat, taken in by food, kidneys maintain balance

Adjust Water Content- taken in in food and drink, lost by urine, sweat and air breathed out (Can't controlled air breathed out).

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Controlling Blood Sugar

Insulin controls this

Blood glucose too high- insulin added which makes liver store glucose

Blood glucose too low- insulin not added so liver releases glucose

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Insulin and Diabetes

Insulin discovered by Banting and Best- Removed pancreas from dog and put an extract into a diabetic dog and the dog's blood sugar level dropped.

Diabetes can be controlled by regular injections of insulin- now made by genetic engineering

Diabetes type 1 is where the pancreas stops making enough insulin, so blood sugar levels can rise a lot.

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DNA- Deoxyribose Nucleic Acid

Has instructions to put an organism together

Chromosomes are long molecules of DNA and a gene is a section of DNA

A gene has the instructions to make a specific protein and they say the order to put the amino acids in, and this determines what type of cell it is

Everyone has unique DNA like fingerprints for police investigations

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Used to make new cells for growth and repair

When a cell reproduces itself by splitting to form two identical offspring.

Asexual reproduction uses this

  • The cell copies its DNA and forms "X" shaped chromosomes,
  • the chromosomes line up at the centre and cell fibres pull them apart,
  • the two arms of each chromosome go to opposite ends,
  • membranes form around each set of chromosomes (these become the nuclei of the 2 new cells),
  • then the cytoplasm divides
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Produces cells which have half the normal number of chromosomes.

Gametes have half the usual number of chromosomes

Used in sexual reproduction

  • Duplicates its DNA, each arm is a copy of the other
  • Pairs line up in centre
  • Cells pulled apart, each cell has one copy of each chromosome, some of Dad's and some of Mum's in each cell
  • Mixture of parents' chromosomes means variation in offspring
  • Chromosomes line up in centre again and the arms are pulled apart
  • Then you have 4 gametes with only a single set of chromosomes in it
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Stem Cells

Embryonic stem cells can turn into any type of cell- they are undifferentiated and develop depending on instructions they're given

Stem cells could cure many diseases- eg. bone marrow transplants which contain stem cells and can turn into new blood cells to replace old ones

Some people against stem cell research because human embryos used have the potential to be human life

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X and Y Chromosomes

Control whether you're male or female, 23 matched pairs of chromosomes in every human body cell, the 23rd pair are labelled XX or XY

All men have XY (Y is Male)

All women have XX (XX is female)

In sperm there's 50% it gets an X and 50% it gets a Y when it is drawn apart at first in meiosis. Similar in eggs but the orginal has XX so all eggs have X.

50:50 ratio of having boy or a girl

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The Work of Mendel

Austrian monk who did genetic experiments with pea plants

He showed that:

  • "Hereditary units" determine characteristics in plants
  • One unit is passed on from each parent
  • They can be dominant or recessive

"Hereditary units" are GENES.

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Possible Genes

Alleles are different versions of the same gene

Most of time you have 2 copies of each gene, 1 from each parent

If different alleles only 1 might be shown in the organism, the dominant will show and the other is recessive.

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Genetic Disorders

Cystic Fibrosis- caused by a recessive allele, disorder of the cell membranes and the body makes a lot of mucus in the air passages and pancreas. People with one copy of allele are carriers. You need 2 of the alleles to be a sufferer

Huntington's- caused by a dominant allele, disorder of the nervous system results in shaking, erratic body movement and severe mental deterioration. A carrier will be a sufferer.

Embryos can be screened for genetic disorders- good as stops suffering and treating disorders costs the government a lot of money, bad as people will want to pick the "perfect child" and rejected embryos are destroyed which could be human life.

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