What cells do all living cells have?

1. A nucleus - Controls what the cell does and contains genetic information.

2. Cell Membrane - Controls movement in and out of the cell

3. Cytoplasm - Where most chemical reactions take place. May have mitochondria in.

4. Ribosomes - Where proteins are made (protein synthesis)

5. Mitochondria - Where most of the energy is released during respiration

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Specialised cell

A cell that has a structure adapted to suit the particular job it does.

 1. Root hair cells have tiny hair-like structure = large surface area for water to move into the cell. Also, have a large permanent vacuole - the movement of water from the soil to root cell. Thirdly, always positioned close to xylem tissue - carries water to rest of plant.

2. Sperm cells have long tails to swim towards the egg, Middle section full of mitochondria to provide energy, digestive enzymes in acrosome to break down layers of the egg and a large nucleus to pass on genetic information.

3. Cone Cells from Human Eyes have visual pigment in the outer section, mitochondria in the middle section to give the visual pigment energy to reform and finally a synapse connected to the optic nerve which carries nerve impulses to your brain so you can see.

All specialised cells when grouped together turn into tissue, which can then turn into organs, which then can become organ systems and eventually make up your whole body

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What factors speed up diffusion?

If there is a big difference in concentration between the two areas, then diffusion happens more quickly.

If the temperature is higher, the particles have more energy and move faster, therefore the rate of diffusion is increased.

Where does diffusion happen in the body?

Diffusion happens in the cells. Many important substances can move across the membrane of the cell by diffusion, including water, amino acids and glucose.

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What is 'net movement?'

The overall movement through diffusion. You work it out by subtracting the number of particles moving out from the number of particles moving in.

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Why do some cells have infolding cell membranes?

To make diffusion easier and more rapid, as it makes a bigger 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 allows small molecules such as water to pass through but doesn’t allow larger particles through
  • Water moves into and out of cells by osmosis
  • In osmosis, water moves against the concentration gradient, so it is similar to diffusion
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Osmosis in Animals

  • If a cell uses up water in due to the chemical reactions in the cytoplasm, then the cytoplasm will become more concentrated and therefore more water will come in by osmosis
  • Similarly, if a cell produces water due to chemical reactions, the cytoplasm will become dilute and therefore it will lose water by osmosis
  • However, osmosis may cause problems in animal cells as well:
    • If a solution outside the cell is more dilute than the cell’s contents, the cell will fill up with water and  will swell up and may burst
    • If a solution outside the cell is more concentrated than the cell’s contents, water will leave the cell by osmosis and the cytoplasm will become too concentrated and it may shrivel up
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Osmosis in Plants

  • Osmosis is important in plants as well
  • Plants gain water through the roots
  • This water moves into cells by osmosis
  • As the cells swell up, they become turgid (stiff)
  • Therefore, they’re able to hold the plant upright
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  • Diffusion – the movement of particles from an area of high concentration to an area of low concentration
  • Diffusion occurs in both liquids and gases
  • The bigger the difference in concentration, the faster the rate of diffusion
  • This is how the smell of cooking travels around the house from the kitchen
  • The difference between two areas of concentration is called the concentration gradient
  • Diffusion is also affected by temperature. Increasing the temperature makes the particles move faster and therefore diffusion will be quicker.
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Animal and Plant cells

Animal Cells contain the following:

  • Nucleus – contains genetic material
  • Cytoplasm – where most chemical reactions take place, controlled by enzymes
  • Cell Membrane – Holds the cell together
  • Mitochondria – Where respiration takes place
  • Ribosomes – Where proteins are made (protein synthesis)

Plant Cells contain the entire above plus:

  • Cell Wall – made of cellulose, supports and strengthens the cell
  • Chloroplasts – contains chlorophyll for photosynthesis
  • Permanent Vacuole – contains cell sap (keeps the cell turgid)
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circulatory system

The circulatory system

  1. The heart is a double pump – Arteries take blood away from the heart while veins take blood to the heart. The right (left as you look at the diagram, right in real life) takes deoxygenated blood to the heart, while the left takes oxygenated blood around the body.
  2. Arteries carry blood at high pressure
  3. As a rule, arteries carry oxygenated blood while veins carry deoxygenated blood. However, the pulmonary vein and artery break this rule and carry the opposite type of blood.
  4. The arteries split off into thousands of tiny capillaries and take blood to every cell
  5. The veins transport the deoxygenated blood at low pressure back to the heart.
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Blood vessels


  • Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes to the lungs)
  • Have thick muscular walls - to withstand pressure
  • Have small passageways for blood (internal lumen)
  • Contain blood under high pressure


  • Carry blood to the heart (always de-oxygenated apart from the pulmonary vein which goes from the lungs to the heart)
  • Have thin walls
  • Have larger internal lumen
  • Contain blood under low pressure
  • Have valves to prevent blood flowing backwards
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Blood vessels


  • Found in the muscles and lungs
  • Microscopic – one cell thick
  • Very low blood pressure
  • Where gas exchange takes place. Oxygen passes through the capillary wall and into the tissues, carbon dioxide passes from the tissues into the blood
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The heart

In the heart, the valves are to prevent the backflow of blood (See diagram for more information). The heart pumps in three stages

  1. Blood flows into the two atria
  2. The atria gently push the blood into the ventricles (the sphincter muscles which let the blood into the atria from the vena cava and pulmonary vein close to stop blood flowing back out).
  3. The ventricle contracts pushing blood around the aorta and pulmonary artery. The valves stop backflow

NB – The left side of the heart has a thick muscular wall because it needs to pump blood around the whole body

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Useful words

  • Bicuspid valve – The valve between the left atrium and left ventricle
  • Tricuspid valve – The valve between the right atrium and ventricle
  • Heart tendons/heart strings – are attached to the valves and stop them flipping inside out
  • Septum – Muscular wall between the right and the left of he heart
  • Semi lunar valves – the valves between the right ventricle and the pulmonary artery
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Red blood cell
Contain haemoglobin which carries oxygen
Made in the bone marrow. The more you train the more red blood cells are made.
Have no nucleus to allow more space for oxygen
Biconcave disc shape - greater surface area and allows cell to move through small spaces

White blood cells
Protect the body by fighting disease

Fluid part of blood
Carries carbon dioxide, hormones and waste

Clump together to form clots
Protect the body by stopping bleeding

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Active transport

Active Transport  - This allows cells to take in substances through a Partially-Permeable Membrane against the concentration gradient because they are in short supply. 

To enable 'Active Transport' to work, energy released from respiration is required. 


   Cells are able to absorb ions from dilute solutions such as -

  • Root Cells absorbing mineral ions from the dilute solutions in the soil. These are in a dilute solution but needed for the plants life
  • Glucose can be re-absorbed from the Kidney tubule via Active Transport as the enrgy is needed for the body to function.

Remember Active Transport needs energy. Osmosis and diffusion don't.  

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Exchange of Materials - 1.4 Exchanging Materials -

Like most complex organs the lungs have a special exchange surface e.g. solutes are absorbed by the intestine, oxygen is absorbed by the lungs and CO(2) removed from them. 

To be an efficient exchange surface you have to have - 

  • a large surface area
  • thin walls (usually one cell thick) or a short diffusion path
  • an efficient transport system - in animals this is the blood circulatory system. 

The lungs contain the 'Gaseous Exchange Surface'. To increase the surface area of the lungs it contains alveoli (air sacs). Alveoli have thin walls, a large surface area to volume ration and a good blood supply. Oxygen diffuses into the many capillaries surrounding the alveoli and carbon dioxide diffuses back out into the lungs to be breathed out. 

To keep a steep diffusion gradient the lungs are ventilated. 

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Exchange of Materials - 1.7 Exchange in the gut

Food is digested in the gut into small soluble molecules that can be absorbed into the blood in the small intestine.

To help this villi line the small intestines walls and are the exchange surface for food molecules. They - 

  • greatly improve the surface area
  • have very thin walls and there are a number of capillaries
  • soluble products can be absorbed into the villi via active transport or diffusion. 

Tip - always relate the features of an exchange surface e.g. alveoli in the lungs, villi in the small intestine. 

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Exchange of Materials - 1.8 Exchange in Plants

Stomata - 

  • Gases diffuse in and out of these holes on a leaves surface
  • The size is controlled by the guard cells surrounding them 
  • Oxygen - needed for respiration and is a waste product of photosynthesis
  • Carbon dioxide - needed for photosynthesis and is a waste product of respiration.
  • Plants also lose water through the stomata due to evaporation in leaves. 

Due to thin, flat shape of leaves, gases don't need to diffuse very far. There are also internal air spaces. 

Root hair cells increase the surface area of the roots so increased amounts of water and minerals are absorbed into the plant. If plants lose water faster than it is replaced by the roots then the stomata close up to prevent the plant from withering. 

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Exchange of Materials - 1.9 Transpiration

Transpiration Stream - The movement of water through plants. Plants take up water via the roots. This goes through the plants to leaves. In leaves the water evaporates and leaves the plant as a gas through the stomata. 

Evaporation/Transpiration is more rapid in dry, hot, windy or bright conditions. 

Evaporation/Transpiration is less rapid in wet, cold, still or dark conditions. 

To prevent excessive water loss Guard cells close up the stomata. 

Wilting also reduces water loss because the leaves collapse and hang down which reduces surface area. 

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Transporting Materials - 2.1 The Circulatory Syste

The Human circulatory System consists of blood vessels, the heart and the blood. 

  • The Heart - a muscular organ which consists of two pumps. These pump blood around the body.
  • Right Pump - forces deoxygenated blood to lungs where it gets oxygen and loses CO(2). Blood                     returns to the heart 
  • Left pump - pumps oxygenated blood around the body. This pump is bigger than the other.
  • Aorta - carries oxygenated blood around the body. On left-hand side of the heart. (If its a diagram it may be a mirror image this is hard to explain look at the diagram in your book).
  • Pulmonary vein - brings oxygenated blood from lungs
  • Left pump - consists of the left atrium, left ventricle and heart valves. The heart muscle wall is thicker on this side than the right, 
  • Vena Cava - brings deoxygenated blood from body to heart. 
  • Pulmonary Artery - takes deoxygenated blood from heart to lungs to get oxygen
  • Right pump - consists of the right atrium, right ventricle and heart valves. 
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Transporting Materials - 2.5 Transport Materials i

Plants have separate transport systems. 

Xylem - 

  • Transports water and mineral ions from the roots to the stem, leaves and flowers. 
  • That water that moves through the Xylem forms 'The Transpiration Stream'
  • It is mono-directional (water only goes in one direction - upwards)

Phloem Tissue - 

  • Carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs. 
  • Bi-directional. 
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Keeping Internal Conditions Constant - 3.1 Control

Homeostasis - The act of keeping conditions controlled within in a narrow range. In the body temperature, blood glucose, water, ion content and levels of waste product are all controlled via Homeostasis. 

Waste Products Removed include - 

  • Carbon dioxide - produced in respiration and removed via the lungs when we breathe out.
  • Urea - produced in the liver from the breakdown of amino acids and removed by the kidneys in the urine (temporarily stored in bladder). 

Water and ions enter the body when we eat and drink. If the water or ion content in the body is wrong, too much water may move in or out of cells - this could damage or destroy cells. 

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Keeping Internal Conditions Constant - 3.2 The Hum

Kidneys - Filter the blood removing excess products and waste products and leaving out the products your blood needs.

The Production of Urine -

  • 1. Filter the blood
  • 2. Reabsorb all the sugar back into the blood
  • 3. Reabsorb all the dissolved ions the body needs back into the blood 
  • 4. Reabsorb as much water as the body needs
  • 5. Release urea, excess ions and water in the urine.
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Keeping Internal Conditions Constant - 3.5 Control

The core body temperature must be kept stable. It is monitored by the Thermoregulatory Centre in the brain - receptors detect the temp of blood flowing through the brain. Temperature receptors in the skin also send signals to the brain about skin temperatures. 

To cool the body down - 

  • Blood vessels near the skin dilate to allow more blood to flow through the capillaries their. Energy is transferred by radiation and the skin cools. Vasodilation. 
  • Sweat glands produce sweat. The water evaporates from the skin surface. The energy required for the water to evaporate comes from the skin's surface - so we cool down

To heat the body up - 

  • Blood vessels constrict so there is a lack of blood flow near the skin. Less energy is radiated. Vasoconstriction
  • We 'shiver'. Muscles quickly contract. this requires respiration and some of the energy released warms the blood.  
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Keeping Internal Conditions Constant - 3.7 Control

The pancreas monitors and controls the level of blood sugar in our blood. 

Too much and the pancreas makes insulin - this causes the Glucose to move from the blood into the cells.

In the liver excess glucose is converted to Glycogen for storage. 

Type 1 Diabetes - When no (or little) Insulin is produced by the Pancreas and the blood sugar level becomes too high. It can be controlled by injections of Insulin and careful monitering of diet and exercise.

If however there is too much Insulin and the blood levels fall too much the pancreas detects this and releases Glucagon, another hormone. This causes the Glycogen in the liver to convert back into Glucose and is released back into the blood. 

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Keeping Internal Conditions Constant - 3.8 Treatin

Type 1 Diabetes is treated with human Insulin made by genetically engineered bacteria. Before every meal, the diabetic must inject Insulin. 

Some use pumps and can adjust the level of insulin injected by the pump. 

Doctors and other scientists are trying to develop new methods of treating and possibly curing Type 1 diabetes. These include - 

  • Pancreas transplants
  • Transplanting Pancreas cells
  • Using embryonic stem cells to produce insulin-secreting cells
  • Using adult stem cells from diabetic patients
  • Genetically engineering pancreas cells to make them work properly

Type 1 Diabetes is treated with human Insulin made by genetically engineered bacteria. Before every meal, the diabetic must inject Insulin. 

Some use pumps and can adjust the level of insulin injected by the pump. 

Doctors and other scientists are trying to develop new methods of treating and possibly curing Type 1 diabetes. These include - 

  • Pancreas transplants
  • Transplanting Pancreas cells
  • Using embryonic stem cells to produce insulin secreting cells
  • Using adult stem cells from dabetic patients
  • Genetically engineering pancreas cells to make them work properly
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How Humans Can Affect the Environment - 4.2 Land a

  • Water Pollution - 
  • Herbicides, pesticides and chemical fertilisers all get washed into rivers and streams by rain.
  • Fertilisers and untreated sewage can cause a high level of nitrates in the water. 
  • Toxic chemicals from landfill also leak into the waterways and pollute the water killing organisms such as fish.
  • Land Pollution - 
  • Sewage - it must be treated properly to remove gut parasites and toxic chemicals or these can get onto the land. Contains human body waste and wastewater. 
  • Landfill waste (household and industrial waste) can let toxic chemicals leak out. Radioactive waste, in particular, is very hazardous.
  • Farming methods pollute the land
  • Herbicides and Pesticides are poisons. They easily get into the food chain harming animal life. Lots are also washed into rivers
  • To keep soil fertile, farmers use chemical fertilisers which get washed into 
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How Humans Can Affect the Environment - 4.3 Air Po

  • Anything burns fuels will produce an acidic gas ( often Sulfur Dioxide) e.g. factories and cars. 
  • This Sulfur Dioxide then dissolves in the water vapour in the atmosphere forming an acidic solution
  • This then falls as Acid Rain. Often acid rain occurs a long way away from the gas was produced simply because of winds. 
  • Acid rain kills organisms e.g. trees.
  • Acid rain can change the soil pH which can damage roots and release toxic materials e.g. aluminium ions are released which also damages organisms in the soil and in waterways. 
  • Enzymes which control reactions are very sensitive pH (acidity or alkalinity) 
  • When trees are damaged, food and habitats for many other organisms are lost. 
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How Humans Can Affect the Environment - 4.4 Defore

Deforestation - Multiple trees are cut down. In tropical regions, large-scale deforestation occurs because of the need for timber and agricultural land.

  • It has - 
  • Increased the release of CO(2) due to burning and decay of trees.
  • Reduced the rate of CO(2) being extracted from the air via photosynthesis. 
  • Reduced biodiversity due to a loss of habitat/food.
  • It occurred so that - 
  • Crops can be grown to produce ethanol-based biofuels.
  • There can be increases in cattle and rice fields for food.
  • Problems - 
  • Cattle and rice produce excessive methane (in the agricultural land).
  • Destruction of peat/peat bogs results in CO(2) being released into the atmosphere. Happens because the peat is removed from the bogs and used as compost. The compost is decayed by micro-organisms
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How Humans Can Affect the Environment - 4.5 Global

Carbon Dioxide is sequestered by plants and water. This means that it is taken in and stored by them. Normal balance in the environment means that CO(2) is taken in by plants and released by respiration and decay. 

Levels of CO(2) and Methane are increasing in the atmosphere. They are greenhouse gases and cause the greenhouse effect. 

An increase in Earth's temperatures (by only a few degrees) will -

  • Cause big changes in the Earth's climate.
  • Cause a rise in sea level due to melting of ice caps and glaciers
  • Reduce biodiversity
  • Cause changes in migration patterns e.g. birds
  • Result in the distribution of species. 
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How Humans Can Affect the Environment - 4.6 Biofue


Biofuels are made from natural products. Two types are ethanol-based Biofuels and Biogas. 

  • Ethanol-based fuels are made via fermentation
  • Micro-organisms respire anaerobically to produce Ethanol using sugars from crops as the energy source.
  • Glucose is produced from maize starch by the action of a carbohydrase.
  • The glucose and sugar cane juices can be fermented by yeast to produce ethanol.
  • The ethanol is extracted by the process of distillation and can then be used as a fuel in motor vehicles
  • Using ethanol as a fuel could replace fossil fuels in the future. In terms of the 'greenhouse effect' using ethanol as a fuel is much more 'carbon friendly'.
  • Ethanol is described as carbon neutral because only the carbon dioxide used for photosynthesis by the crops is returned to the atmosphere when the ethanol is burned. 
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How Humans Can Affect the Environment - 4.8 Making


Short Food chain = less energy wasted. - This means it is more efficient for us to eat plants than to eat animals. 

We can produce meat efficiently by - 

  • Preventing the animal from moving so it doesn't use energy. This, however, is cruel and many people view it as controversial. 
  • Keeping the animal in the warm shed so it doesn't use as much energy keeping warm. 
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How Humans Can Affect the Environment - 4.9 Sustai

Sustainable Food Production - Involves managing resources and finding new types of food such as mycoprotein. This ensures there's enough food for the population and the future. 


  • Fish stocks in the ocean are monitored
  • Fishermen can only remove a strict allocation of fish per year (a quota) and must use certain sized nets to avoid catching small, young fish. 


  • The fungus, Fusarium, is grown to produce mycoprotein - a protein-rich food suitable for veggies. Grown aerobically on cheap sugar syrup made from waste starch and the mycoprotein harvested.
  • Micro-organisms can be grown on a large scale in industrial fermenters
  • The conditions in a fermenter must be controlled to ensure maximum growth of the Fusarium.
  • Industrial fermenters are large vessels which have - an oxygen supply for resp., stirrers or gas bubbles to evenly distribute microbes, a water-cooled 
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How Humans Can Affect the Environment - 4.10 Envir


Human activities that can affect the global environment include - 

  • Deforestation - increased levels of CO(2)
  • Increase in rice growth and cattle cultivation causing an increase in methane. 
  • Building dams - loss of habitat, drying out of rivers, reduction in fertile soil for crops.

The issue of Global Warming divides opinion. Some think the greenhouse effect has caused the increase in temperature, others think it is part of a natural cycle. 

There is a lot of data to support both arguments made in different countries, it can also be noted that ensuring the validity of this data is difficult. Scientists also come to different conclusions based on the same data. These explanations can be biased and opinionated. 

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