WJEC Biology 2 higher

Revision notes for the Biology 2 section fo the WJEC science course. sorry for any spelling mistakes, it takes too long to double check them all...

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Biology 2
Cells
The nucleus is the control centre of all cell activity. The nucleus contains the chromosomes that are important in cell division.
Chemicals outside the nucleus make up the cytoplasm. Cytoplasm is enclosed by a cell membrane that separates the cell from
other cells and surrounding fluids, it is a semi permeable membrane, like the membrane of the nucleus. Molecules can pass
through in a controlled manner. It allows something through but not everything,
Plant cells
The cell wall is made of cellulose. This is a thick rigid non living layer around the cell membrane that helps the plant to
support its self. It is permeable.
Vacuole- fluid filled space surrounded by a membrane. The fluid contains dissolved food materials, minerals and waste
products. Main function is to support the cell through the pressure of the fluid.
Chloroplasts are green discs that contain the green pigment chlorophy ll which is essential for the process of
photosynthesis. Only present in parts of the plant that are exposed to light.
Cell division- mitosis. Causes growth in animals and plants. In animals, all tissues undergo mitosis and some stage in
their development. Some tissues can perform mitosis better than others e.g. skin. Animals are able to repair most
damages tissues using mitosis.
In plants, the parts that undergo mitosis are limited to growing areas. At the tips of the roots and stems there are the
areas of growth where mitosis happens; meristems.
Plants have the ability to grow new parts whereas animals generally can't.
The size to which plants grow depends on- the ability to support them to have access to sunlight and the maximum
height water can be transported.
The size to which animals grow depends on- the ability to support themselves so that they can move and the efficiency
of getting oxygen to the cells that release energy.
Specialisation
The fate of most cells is decided form a very early stage of development. Fertilisation causes mitosis to begin. The cell
divides again and again until it forms hundreds of cells.
Most cells in your body are specialised for aparticular job. For example, whie blood cells are brilliant at foighting
infections but cant carry oxygen like a red blood cell.
Differentiation is the process by which a cell changes to become specialised for its job. In most animal cell, the ability to
differentiate is lost at an early stage, but loots of plant cells dont ever lose the ability.
Some cells are undifferentiated and unspecialised. They can develop into different types of cell depending on what
instructions theyre given. These cells are called stem cells.
Scientists can take these cells and grow them into different tissues which could be used to replace damages tissue in
critically ill patients.
The technology is controversial because it involves taking cells from the cluster of embryonic cells. This could destroy
the embryo.
Stem cells donated by adult are being investigated to see if they can do the same purpose. They are found in bone
marrow.
Used for; replacing damages tissue, treating serious illnesses, testing drugs, screening toxins, testing gene therapy
methods
The fate of most cells is decided form a very early stage of development. Fertilisation causes mitosis to begin. The cell divides
again and again until it forms hundreds of cells. When tissues and organs start to develop, they form from cells that become
specialised into, e.g. muscle, liver, kidney and skin cells.
Enzymes

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Enzymes are proteins made by living organisms that speed up the rate of reactions without losing their properties and becoming a
product. They are catalysts. They can be extracted from organisms and still keep their properties. Enzymes are used in biological
washing powders and in certain food manufacturing processes.
Most enzymes are involved in the release of energy in the process of respiration.
All enzymes have certain properties;
They are proteins
They are denatured when they are heated above optimum temperature.…read more

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Substances enter and leave cells through the cell membrane
Digested food and oxygen are among the essential materials to be taken into cells. Waste products such as carbon dioxide must
be removed. All materials going in or out of the cell must pass the cell membrane. Some molecules can pass through freely, and
others can't pass through. The membrane selects materials for entry and exit.…read more

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Tube 2- filled with distilled water, placed in 5% sucrose solution
Tube 2 will have decreased in mass because there is a lower concentration of water outside the tube. This means that the water
would move from the high concentration to the low concentration through osmosis.
The effects of osmosis on...…read more

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Minerals ;
o Iron- liver and read meat- making haemoglobyn
o Calcium- milk and cheese- making teeth and bones
o Sodium- salt ­ proper function of nerves
o Fluoride- milk + toothpaste- hardening tooth enamel.
Roughage (dietary fibre) ­ veg, fruit, cereal ­ keeps everthign flowing smoothly through the digestive system
Water- anything soggy + water- without water, cells die and theorganism dies very uickly
Carbohydrates
They are mainly fuels from which your cells release energy. The energy is released through respiration.…read more

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Layers of muscle line the walls of the oesophagus, squeezing the food to move to the stomach.
The stomach
Pummels the food with its muscular walls
It has a thick lining with many glands. It twists, squeezes and churns the food.
There are three types of glands secreting; digestive enzymes, hydrochloric acid and mucus.…read more

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We can't break downs cellulose, so we can't put on weight form eating it. We eat veg as the fibre gives your digestive muscles
something to press on to move the food through your body. Otherwise, it would stay in your body and go off.
Enzymes involved in digestion- break down big molecules into small molecules
Amylase ­
carbohydrate e.g. starch- into glucose- breaks down chains into single pieces of glucose.
Protease-
acid creates the optimum pH0 (in the stomach).…read more

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Girls generally have a growth spurt before boys (reach puberty first) but growth during puberty is at the same rate for both.
How does growth rate differ with different parts of the body?
Alometric growth.
In a foetus, the brain and head grow quickly then gradually slow down, and the arms and legs grow slowly at the beginning then
get faster.
Humans
Humans start as one single cell called a zygote (fertilised egg cell). The zygote starts to divide by exponential growth into
stem cells.…read more

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Photosynthesis= carbon doxide + water sunlight + chlorophyll Glucose and oxygen
Energy is released from food and is one of the basic needs of all living things. Energy contained in food is released and used in the
living organism. Therefore, to remain alive, the organism must be supplied with fuel in the form of food.
Plants get their energy through the process f photosynthesis
4 factors can affect photosynthesis;
Light
Carbon dioxide
Temperature
Chlorophyll.…read more

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Energy and nutrient transfer
Plants are the first links in all food chains because they are producers- they change the energy in sunlight into stored chemical
energy. When plants are eaten by herbivores, some of the energy is passed to the consumers in the food chain. The energy
passes in this way from consumer to carnivore, to scavengers and decomposers which feed on dead organisms.
However not all the energy stored by e.g. an herbivore is stored by e.g. the carnivore hat feeds o it.…read more

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