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Additional Biology Key Points
Most animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
Plant cells contain all the structures seen in animal cells as well as a cell wall and, in many cases
chloroplasts and as permanent vacuole filled with sap.
Enzymes control the chemical reactions inside cells.
Cells may be specialised to carry out a particular function.
Examples of specialised cells are fat cells, cone cells, root hair cells and sperm cells.
Dissolved substances move in and out of cells by diffusion, osmosis and active transport.
Diffusion is the net movement of particles form an area of high concentration to an area where they
are at a lower concentration.
Osmosis is a special case of diffusion
Osmosis is the movement of water from a high water concentration (dilute solution) to a low water
concentration (concentrated solution) through a partially permeable membrane.
Photosynthesis can be summed up by the equation:
Carbon dioxide + water [+light energy] glucose + oxygen
During photosynthesis light energy is absorbed by the chlorophyll in the chloroplasts. It is used to
convert carbon dioxide and water into sugar. Oxygen is released as a by product.
Leaves are well adapted to allow the maximum photosynthesis to take place.
There are three main factors that limit the rate of photosynthesis- light, temperature and CO2 levels.
We can artificially change the environment in which we grow plants. We can use this to observe the
effect of different factors on the rate of photosynthesis. We can also use it to control their rate of
Plant cells use some of the glucose they make during photosynthesis for respiration.
Some of the soluble glucose produced during photosynthesis is converted into insoluble starch for
Plant roots absorb mineral salts including nitrate needed for healthy growth.
Nitrates and magnesium are two important mineral ions needed for healthy plant growth.
If mineral ions are deficient, a plant develops symptoms because it cannot grow properly.
Radiation from the sun is the main source of energy for all living things. The suns energy is captured
and used by plants during photosynthesis.
The mass of living material at each stage of a food chain is less than at the previous stage. The
biomass at each stage can be drawn to scale and shown on a pyramid of biomass.
The amount of biomass and energy gets less at each successive stage in as food chain.
This is because some material is always lost in waste, and some is used for respiration to supply
energy for movement and for maintaining the body temperature.
Biomass and energy are lost at each stage of a food chain. The efficiency of food production can be
improved by reducing the number of stages in our food chains it would be most efficient if we all just
If you stop animals moving about and keep them warm they lose less energy. This makes food
production much more efficient.
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Living organisms remove materials from the environment as they grow. They return when they die
through the action of the decomposers.
Dead materials decay because they are broken down by microorganisms.
Decomposers work more quickly in warm moist conditions. Many of them also need s good supply of
The decay process releases substances which plants need to grow.
In a stable community the processes that remove materials (particularly plant growth) are balanced
by the processes which return materials.…read more
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Your blood glucose concentration is monitored and controlled by pancreas.
Pancreas produces hormone insulin which allows glucose to move from the blood into the cells.
In diabetes, the blood glucose may rise to fatally high levels because the pancreas does not secrete
enough insulin. It can be treated by injections of insulin before meals.
In body cells, chromosomes are found in pairs.
Body cells divide by mitosis to produce more identical cells for growth, repair, replacement or in
some cases asexual reproductions.…read more