Cells- Animal and Plant


Pyramids of Biomass

Energy Transfer

Food Production

The carbon cycle and decay

Enzymes and digestion


Cell Division


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Animal and Plant cells have:

nucleus- contains genetic material, controls activities of the cell

cytoplasm- most chemical processes take place here; controlled by enzymes

cell membrane- controls movement of substances into and out of the cell

mitochondria- most energy is released by respiration

ribosomes- proteins are made here- (proteinsynthesis)

Plant cells also have-

cell wall- made of cellulose, supports and strengthens the cell

chloroplasts- contain chlorophyll which absorbs light energy for photosynthesis

permanent vacuole- filled with cell sap- (kepps the cell turgid)

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Cells- continued

Single cells- carry out all functions of life; feeding, respiration, excretion and reproduction

Specialised cells- made up lots of cells, carry out particular jobs

Examples of specialist cells- sperm, eggs, red blood cells and nerve cells

Sperm- function is to fertilise an egg cell, head contains genetic info and an enzyme to help penetrate the egg cell membrane, the middle section has mitochondria for energy, the tail moves the sperm to the egg

Red blood cells- thin outer membrane to let oxygen diffuse through easily, its shape increases surface area to allow more oxygen to be absorbed efficiently, No nucleus so the whole cell is full of haemoglobin

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Diffusion and Osmosis

Diffusion- Is the passive movement of particles from an area of high concentration to an area of low concentration.

E.g: The smell of cooking travels around the house from the kitchen by diffusion- Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration.

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

Osmosis is important to plants, they gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them stiff so the plant is held upright.

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Plants- Photosynthesis

Green plants absorb light energy by using chlorophyll in there leaves- they use it to react CO2 with H2O to make a sugar called glucose. The glucose is then used in respiration, or made into starch and stored, Oxygen is produced as a by-product.

carbon dioxide + water (+light energy) ---> glucose + oxygen

temperature, CO2 concentration and light intensity are all factors that can limit the rate of photosynthesis.


Light- from the sun                                                                                   Chlorophyll- absorbs energy in sunlight                                                         Carbon dioxide- enters leaf from surrounding area                                             Water- comes from soil, up the roots and into the leaf

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Some farmers use artificial light (paraffin lamps) to increase crop growth in greenhouses. They use this so that photosynthesis can contiue during the night

Plants make glucose when they photosynthesise, glucose that is not used is then used in other ways;

Respiration- plants make glucose in there leaves , which is used for respiration, releasing energy. This then enables them to convert the rest of the glucose into other useful substances.                                                 Making fruit- glucose, along with fructose is turned into sucrose for storing in fruits.                                                                                                     Making cell walls- glucose is converted into cellulose for making cell walls                                                                                                           Making proteins- glucose is combined with nitrates to make amino acids, which are then made into protein.                                                                         Stored in seeds- glucose is turned into fats and oils (lipids) for storing in seeds                                                                                                          Stored as starch- glucose is turned into starch and stored in roots, stems and leaves, ready to be used in winter when photosynthesis is not happening.

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Pyramids of Biomass

Reveal the mass of living material at each stage in a chain..

1OO dandelions feed 10 rabbits which feed 1 fox

Each bar on a pyramid of biomass shows the mass of living material at that stage of the food chain.

( The big bar along the bottom always represent the producer, (a plant). The next bar is the primary consumer (the animal that eats the plant). Then the secondary consumer and so on. 

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Energy Transfer

Energy is transferred along food chains from one stage to the next. Not all of the energy availible to organisms at one stage can be absorbed by organisms at the next one. The amount of availible energy decreases. Some of this energy goes into growth and the production off offspring but most is used up in ither ways. These include:

1- Energy released by respiration is used for movement and other things, and is eventually lost as heat to the surroundings.     

2- Energy is lost in waste materials, such as faeces.

Most food chains are quite short because alot of energy is lost at each stage. 

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Food Production

The efficiency of food production can be improved by reducing the amount of energy lost to the surroundings. This can be done by: 1- Preventing animals moving around too much 2- Keeping their surroundings warm Mammals and birds maintain a constant body temperature using energy released by respiration. As a result they lose a lot of energy. Keeping pigs and chickens in warm sheds with little space to move around allows more efficient food production. However, this raises moral concerns about the lives of such animals.

Calculating Energy Efficiency..

 A bull ate 100kj of stored energy (grass) He excreted 63kj (faeces, urine and methane) He has 4kj of energy stored in its body tissue. How much was used up for respiration? 100-63-4= 33kj Only 4kj of the original energy availible to the bull is availible to the next stage. Therefore, the efficience of this energy transfer is (4/100) x100= 4%

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The Carbon cycle and decay

All cells contain carbon, because they all contain proteins, fats and carbohydrates. Plant walls are made of cellulose - which is a carbohydrate

Carbon is passed from the atmosphere, as CO2, to living things, passed from one organism to the next in complex molecules, and returned to the atmosphere as CO2: This is known as the carbon cycle.

Materials from living things decay because microorganisms (detritus feeders) digest them- this process happens faster in warm, moist conditions with plenty of oxygen.

During the decaying process, CO2 is released back into the atmosphere as these organisms respire.

Decay can be very slow in cold, dry conditions and when there is a shortage of oxygen.

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Enzymes and Digestion

Enzymes are biological catalysts. There are optimimum temperatures and PH values at which there activity is greatest. Enzymes are also proteins, and are usually denatured above 45'c

Enzymes are important in respiration and digestion. Aerobic respiration releases energy from glucose. Digestion is the breakdown of carbohydrates, proteins and fats into small soluble substances that can be absorbed into the blood.

Lipases and proteases are used in biological deterrents and enzymes are used in the manufacture of food and drink.

Enzymes are proteins that are folded into complex shapes that allow smaller molecules to fit them.

Enzymes can be de natured by high temperatures or extremes of PH

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