e) Nutrition in Humans

e) Nutrition in Humans 

2.23 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre

A balanced diet gives you all the essential nutrients you need to carry out the life processes, in the right proportions. The essential nutrients you need are: carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibre.

2.24 identify sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D and the mineral ions calcium and iron, water and dietary fibre as components of the diet. 

2.25 understand that energy requirements vary with activity levels, age and pregnancy

You have to eat the right foods in order to get the right amount of energy your body needs. However, this 'right amount' is not the same for everyone, and different people have different energy requirements. For example, the more active somebody is, the more energy they will need as opposed to somebody who is less active, so does not need as much energy. As children and teenagers are growing, they need more energy than older people, also because they are generally more active. Finally, pregnant women will need more energy than other women because as well as energy for their own bodies, they also need to provide energy that their babies need to develop. 

2.26 describe the structures of the human alimentary canal and describe the functions of the mouth, oesophagus,  stomach, small intestine, large intestine and pancreas

The Mouth 

• This is where mechanical digestion happens. (Breakdown of large, insoluble food molecules into small, soluble ones.) This is done through chewing the food with your teeth. 
• Salivary glands in the mouth produce amylase enzyme in the saliva, A bolus (ball of food covered in saliva) is created. This makes it easier for the food to be swallowed and broken down. 

The Oesophagus

• This is the muscular tube that connects the mouth and the stomach. It squeezes the boluses through your gut with a squeezing action (waves of circular muscle contractions) known as peristalsis.

The stomach

• The stomach produces hydrochloric acid so the protease enzyme has the right pH to work at its best ability. This enzyme helps to churn the food in the stomach and pass it through. 

The Pancreas

• Here, protease, amylase and lipase enzymes are produced. They are then released into the small intestine. 

Small Intestine 

• The enzymes produced in pancreas help to complete digestion here. Nutrients are absorbed out of the alimentary canal into the body. 

Large Intestine

• Here, excess water is absorbed from the food. 

Diagram of the alimentary canal (gut). 

2.27 understand the process of ingestion, digestion, absorption, assimilation and egestion. 

1. Ingestion - this is putting food or drink into your mouth. 
2. Digestion - break down of large, insoluble food molecules into smaller, soluble ones by mechanical digestion (teeth and stomach muscles used) or chemical digestion (enzymes and bile used.)
3. Absorption - the process that moves molecules through the walls of the intestines (where digestion takes them), into the blood, with digested food molecules absorbed into the small intestine and water mainly absorbed in the large intestine. 
4. Assimilation - after digested food molecules have been absorbed (in small intestine), they are moved into body cells. They then become part of the cells.
5. Egestion - removal of undigested food from the body as faeces, through the anus. 

2.28 explain how and why food is moved through the gut by peristalsis

Muscular tissue lines the alimentary canal, and this muscular tissue performs a squeezing action, which is waves of circular muscle contractions, known as peristalsis. These contractions help squeeze boluses (balls of food) through your gut - preventing it from getting clogged up as it would do if the boluses did not pass through. That way, digestion would not properly occur so it would be very detrimental to the human body. It is therefore an important process. 

2.29 understand the role of digestive enzymes, to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by by lipases

Digestive enzymes break down large insoluble food molecules, into soluble smaller ones. The molecules they break down are too large to pass through the walls of the digestive system, so they must be broken down in order for digestion to occur. 

• The enzyme amylase converts starch into maltose. This maltose is then converted to glucose by maltose. So, amylase and maltose convert starch to glucose. 
• Proteases convert proteins into amino acids. 
• Lipases covert lipids into glycerol and fatty acids. 

2.30 understand that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid emulsifying lipids

Bile is produced in the liver and then stored in the gall bladder, before being released into the small intestine. In the small intestine, the enzymes work best in alkaline conditions, however the food that it must absorb is acidic after having been in the stomach. Bile is alkaline so it's presence will help the enzymes in the small intestine to work properly and do their job. Also, bile does emulsify fats. This means it breaks the fat into tiny droplets, giving a much bigger surface area of fat for the enzyme lipases to work on, making its digestion faster. 

2.31 describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine 

The small intestine is adapted for the absorption of food. One of the ways it is adapted is that it is very long, so there is time to break down and absorb all the food before it leaves the small intestine, helped because of the very large surface area the small intestine has. 

The walls of the small intestine are covered in millions of tiny projections called villi. The cells on the surface area of these villi then each have their own microvilli, increasing the surface area even more.

 They help the absorption of the products of digestion in this way, as well as their having a single permeable layer of surface cells, allowing molecules to pass through it easily. 

It also has a good blood supply, so molecules can travel around at a faster pace. 

2.32 describe an experiment to investigate the energy content in a food sample 

To find out how much energy food contains, you can burn it. This is known as 'calorimetry' and can be done through the following experiment: 

1. The food you are burning should be able to burn easily - ie. a dry food, like peanuts or pasta. 
2. Weigh a small amount of food and then skewer it on  mounted needle. 
3. Then, set up a boiling tube to be held with a clamp (securely, in place.) Add 25cm^3 of water to the tube. This will be used to measure the amount of heat energy that is released upon the food being burnt. 
4. Measure the initial temperature of the water, then use a Bunsen burner flame to set fire to the food.
5. Immediately hold the now burning food under the boiling tube, until the flame goes out. Then relight the food and hold it under the tube, again until it goes out. Continue to do this until the food will not catch fire again. 
6. Lastly, measure the final temperature of the water (now that your food will no longer catch fire.)
7. Then, the following equation must be used in order to calculate the amount of energy in the food. 

• Energy in food (J) = Mass of water (g) x Temperature change of water (degrees celcius) x 4.2, 

Substituting into the equation, mass of water (g) = 25, temperature change of water can be deduced from the temperature results of the experiment (subtract the smaller from the larger to find the change,) and the 4.2 signifies the amount of energy (in joules) needed to raise the temperature of 1g of water by 1 degree celcius. The result of this equation will give you the amount of energy in joules. To find the amount of energy un joules per gram so you can compare the energy content of other foods, you would use the following equation; 

• Energy per gram of food (J/kg) = energy in food (J)/mass of food (g)
• The energy released from burning is lost in the surroundings during this experiment, so to make the experiment as accurate as possible, you can insulate the boiling tube with foil, which would minimise heat loss and keep more energy in the water. 

e) Nutrition

2.17 describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy

Photosynthesis is the process that uses energy (from the sunlight) to create food for itself in the form of glucose. The process occurs inside the chloroplasts of the plant (inside the leaf), which contains a pigment called chlorophyll that absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. Oxygen is also produced. It is an important process because it converts light energy to chemical energy. which is then released during respiration. 

2.18 write the word equation and the balanced chemical symbol equation for

photosynthesis
                                                           (sunlight)                    

   carbon dioxide      +       water            >             glucose       +    oxygen 

                                                         (chlorophyll) 

         6CO2                 +        6H2O        >           C6H12O6      +    6O2

2.19 understand how varying carbon dioxide concentration, light intensity and

temperature affect the rate of photosynthesis

Carbon dioxide concentration

CO2 is a raw material needed in the process of photosynthesis. If there is too little carbon dioxide present, then the rate of photosynthesis will slow down.  Increasing the concentration of CO2 will also increase the rate of photosynthesis up to a point, until CO2 will no longer be the limiting factor and it will instead be the temperature or the light intensity. 

Light intensity 

Not enough light slows down the rate of photosynthesis. Chlorophyll uses light energy to perform photosynthesis so it can only take place at the rate that light energy is arriving. If the light intensity is increased, the rate of photosynthesis will increase steadily along with it until it reaches a certain point, where the light intensity will no longer make a difference. Instead, it will be either the CO2 level or the temperature which will be the limiting factor (stop photosynthesis from happening any faster.) 

Temperature

The temperature has to be just right in order for the rate of photosynthesis to increase. As the temperature increases, the rate of photosynthesis will also increase but again, only up to a certain point (usually around or above 45 degrees celcius.) This is because the temperature affects the enzymes involved, which are denatured when heated past 45 degrees, making the rate of photosynthesis rapidly decrease. However, it is normally the temperature being too low that is the limiting factor. 

2.20 describe the structure of the leaf and explain how it is adapted for photosynthesis

The structure of leaves is geared towards making photosynthesis as achievable and effective for the plant as possible. 

• Leaves are broad, so there is a large area exposed to the sunlight that the plant needs in order for photosynthesis to occur. 
• Majority of the chloroplasts are found in the palisade mesophyll layer, so they are close to the top of the leaf and therefore receive the most sunlight there. 
• The upper epidermis is transparent, light passes through it to the palisade layer. 
• The network of vascular bundles that leaves have contain xylem and phloem (transport vessels). They deliver water and nutrients to every part of the leaf and take away the glucose the leaf produces during photosynthesis. 
• The waxy cuticle of the leaf helps to reduce its water loss by evaporation (water vital for photosynthesis.) 
• Stomata (little holes in base of leaf) let CO2 diffuse directly into the leaf (CO2, or carbon dioxide, also vital for photosynthesis.) 

2.21 understand that plants require mineral ions for growth and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids. 

Plants need certain mineral ions to grow. They get these elements from the soil, and not enough of that particular element will cause a deficiency in the plant. The two examples you need to know: 

Magnesium ions 

- required for making chlorophyll, therefore needed for photosynthesis. 

- not enough magnesium means plants leaves turn yellow. 

Nitrate ions 

- contain nitrogen, which is used for making amino acids and proteins. 

- therefore needed for cell growth, 

- not enough nitrates/nitrogen means plants will be stunted and their leaves will become yellow. 

2.22 describe experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll 

Pondweed can be used for this experiment, in order to measure the effect of light intensity and levels of CO2 and chlorophyll on the rate of photosynthesis. 

1. Place a source of white light at a specific distance from the pondweed. 
2. Having left the pondweed to photosynthesise for a certain amount of time, you will notice that the released oxygen will collect in the capillary tube. 
3. Draw the gas bubbles in the tube up alongside a ruler to measure the length of the gas bubble. (Proportional to amount of CO2 produced.)
4. Then, repeat the experiment with the light source placed at different distances from the pond weed to see how light intensity affects the rate of photosynthesis. Additionally, you could add baking powder to the water, which will increase the CO2 levels, and test a white leaved plant against a green leaved plant (latter will contain chlorophyll.) Measuring the rate of photosynthesis in each case will tell you how each factor affects it. 

d) Movement of substances into and out of cells

d) Movement of substances into and out of cells

2.12 understand definitions of diffusion, osmosis and active transport

• Diffusion = the net movement of particles from an area of higher concentration to an area of lower concentration.
• Osmosis = the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. (Water will move from a dilute solution to a concentrated solution.)
• Active transport = the movement of particles against a concentration gradient, from an area of lower concentration to an area of higher concentration, using the energy released during respiration. 

2.13 understand that movement of substances into and out of cells can be by

diffusion, osmosis and active transport

The three processes are the ways in which substances move in and out of cells. 

Diffusion occurs in both liquids and gases (particles in these can move about freely). Particles travel from an area of higher concentration to an area of lower concentration. This can be as simple as different gases diffusing through eachother, or could also be the process of particles passing through a cell membrane from their area of high concentration to an area of low concentration. 

     

• Osmosis

Osmosis is another way through which substances move in and out of cells. The water molecules pass through a partially permeable membrane (one with very small holes in it, including the cell membrane) and will travel from its region of higher concentration to its region of lower concentration. Water molecules move about randomly all the time, so they both in both directions through the membrane however there will be more water molecules on one side than the other, so there will be a steady flow of water into the region with fewer water molecules (particles travel into area of lower concentration.) 

• Active transport 

Active transport is the third way through which substances move in and out of cells. In this process, dissolved molecules move across a cell membrane from an area of lower concentration to an area of higher concentration, therefore against the concentration gradient (normally molecules travel from area of higher concentration to area of lower concentration.) For example, in the digestive system, if there is a low concentration of nutrients in the gut and a higher concentration of nutrients in the blood, then nutrients will go against the concentration gradient and travel from the area of lower concentration (gut) to the area of higher concentration (blood.) Carrier proteins pick up specific materials and take them through the cell membrane to the area of higher concentration, in this case the blood. Because the particles must go against the concentration gradient, they need energy to do this and this energy can be received by living organisms by respiration. 

2.13 understand the factors that affect the rate of movement of substances into and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient. 

There are three main factors that affect the rate of movement of substances into and out of cells. These are: 

1. Surface area to volume ratio

The rate of diffusion, osmosis and active transport is higher in cells that have a larger surface area to volume ratio. For example, if a cell has a surface area of 24cm^2 and a volume of 6cm^3, then its surface area to volume ration will be 24:6 = 4:1. 

So, this cell would have a faster rate of movement of substances than one that had a smaller ratio, such as a surface area of 36cm^2 and a volume of 18cm^3, which would have a ratio of 36:18 = 2:1. 

2. Temperature 

As the particles in a substance are heated and get warmer, they have more energy so move about faster. So, as the temperature increases, so does the rate at which substances move in and out of cells. 

3. Concentration gradient

This only applies to diffusion osmosis, not active transport. The larger the difference in concentration of the inside and the outside of the cell, the faster the substances move in and out of the cell. If there are lots more particles on one side of the cell, then there are more to move across. (This side will have the larger concentration, bigger difference in concentration and therefore will have substances moving in and out of it at a fast rate.)

2.14 understand the importance in plants of turgid cells as a means of
support

When a plant is well watered, all of its cells will draw in water by osmosis and become plump and swollen. They are said to have become turgid when this occurs. The contents of the cell will push against the cell wall - this is referred to as turgor pressure. It is this turgor pressure that occurs in turgid cells that helps to support the plant tissues. 

2.15 understand the factors that affect the rate of movement of substances into
and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient

Surface area to volume ratio

The rate of diffusion, osmosis and active transport is higher in cells with a larger surface area to volume ratio. 

Temperature 

When the particles in a substance are heated (get warmer), they move around at a quicker pace and have more energy. Therefore, as the temperature increases, substances move in and out of the cells at a faster rate. 

Concentration gradient

This only effects the rate of diffusion and osmosis, it does not affect the rate of active transport. The bigger the difference in concentration between the inside and the outside of the cell, the faster substances move in and out of a cell. This is because if there are lots more particles on one side than the other, there are more to move across. 

2.16 describe experiments to investigate diffusion and osmosis using living and
non-living systems.

Investigating diffusion in a non-living system

• Put a few drops of coloured substance (eg. green food colouring) into a jar of water.
• Time how long it takes for the food colouring to diffuse and for all of the water to be the same colour (translucent green if green food colouring is used). Expect this to happen after roughly two minutes of adding the drops. 
•      In another container, again add a few drops of food colouring but this time to water that is a different temperature from the first.
•      Time how long it takes for the food colouring to diffuse in this second container than in the first. If the heat of the water was raised the second time, the colour will have moved through the liquid faster and therefore have diffused at a quicker rate. If you decreased the temperature the second time, the heat will be lower so the particles will have less energy and the colour will move through the liquid at a slower rate, with the diffusion therefore having a slower rate of reaction.

1.        

Investigating Osmosis in Living Systems

•     Cut a potato into two roughly identical cylinders.
•     Measure the length of each cylinder for later comparisons.
•     Place one cylinder into a beaker that has just pure water in, and the other into a beaker that has salt water.
•     After half an hour or so, remove the potato cylinders from their respective beakers and remeasure them.
•     If the cylinder is now a bit longer than it was before being placed into the beaker, then they have drawn water in by osmosis. If the cylinder is now shorter, then water has been drawn out by osmosis. 

Investigating osmosis in non-living organisms

•       Tie a wire around one end of some visking tubing (= a partially permeable membrane) and put a glass tube in the other end, fixing the tube around it with wire.
•       Pour some sugar solution down the glass tube into the visking tube.
•         Then, put the visking tubing in a beaker of pure water and measure where the sugar solution comes up to on the glass tube.
•      Leave the tube overnight, and the next day measure where the  liquid is in the glass tube.
•     Water should have been drawn into the vi=sking tubing by osmosis and this will therefore force the liquid up the glass tube. 

• 
  
• 
  

c) Biological molecules

c) Biological molecules

2.5 identify the chemical elements present in carbohydrates, proteins and lipids
(fats and oils)

Carbohydrates and lipids (fats and oils) are both made up of the following elements; 

• Carbon 
• Hydrogen 
• Oxygen 

Proteins are made up of the following elements; 

• Carbon 
• Hydrogen
• Oxygen
• Nitrogen
• Sulphur
• Phosphorous 

2.6 describe the structure of carbohydrates, proteins and lipids as large

molecules made up from smaller basic units: starch and glycogen from

simple sugar; protein from amino acids; lipid from fatty acids and glycerol

Starch and glycogen are large, complex carbohydrates that are made up of many smaller units held together in a long chain. These smaller units are 'simple sugars' and examples include; glucose and maltose molecules.

Proteins are made up of long chains of amino acids. 

Fats and oils (lipids) are composed of fatty acids and glycerol. (Glycerol + 3 fatty acids) 

2.7 describe the tests for glucose and starch

Glucose

1.       . Add a few drops of Benedict's reagent to the solution. (Benedict’s reagent is blue and will turn the sample blue.)
2.         Place the test tube in a water bath at around 60/70 degrees celcius from 2-3 minutes. (Make sure the solution doesn’t boil.)
3.        If the test is positive (and glucose is present) then a coloured precipitate will form. (Orange/red for strong solutions of glucose, green for weak solutions of glucose.

Starch

1)      Add a few drops of iodine solution to the test sample of starch you have.

2)      If the sample changes from browny-orange to a dark, blue-black colour, then starch is present.

3)      If the sample remains the same browny-orange colour, then there is no starch present. 

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

Enzymes speed up chemical reactions without being used up in them. They are therefore catalysts (biological catalysts). The reactions that enzymes speed up are very important metabolic reactions, which are defined as: chemical processes that occur in living organisms in order to maintain life. 

2.9 understand how the functioning of enzymes can be affected by changes in

temperature, including changes due to change in active site

All enzymes have an optimum temperature, the temperature at which they function best and their activity is greatest. When this temperature is raised too high, some of the bonds holding the enzyme together will break. This means that the enzyme will lose its shape, and therefore its active site will no longer fit the substrate, so the reaction will stop as the enzyme has been denatured. 

2.10 understand how the functioning of enzymes can be affected by

changes in active site caused by changes in pH

The functioning of enzymes can also be affected by changes in pH. Again, enzymes have an optimum pH at which they work best. If the pH becomes too high or too low for the enzyme, its bonds will break and the active site will change shape. This means that the reaction will stop as the size of the active site has changed, and the enzyme has been denatured. 

2.11 describe experiments to investigate how enzyme activity can be affected by

changes in temperature.

•      Amylase is an enzyme that catalyses the breakdown of starch to maltose.
•      In this experiment, the starch solution and amylase enzyme should be kept in a test tube in a water bath which remains at a constant temperature.
•         Starch is the substrate in this experiment, and it is easy to detect. Pour a few drops of iodine solution into the amylase solution. If starch is present, the iodine solution will change from an orange/brown colour to a blue-black colour.
•      You can then time how long it takes for the starch to disappear by regularly sampling the solution (say every minute or so). Then use the times and the amount of starch present to compare rates between different tests.
•      By adjusting the temperature of the water bath, it will become clear how the temperature affects the activity of amylase when continuing to compare these sampling results with the past results. 

Section 2: Structures and functions in living organisms

Section 2; Structures and functions in living organisms 
a) Levels of organisation

2.1 describe the levels of organisation within organisms: organelles, cells,
tissues, organs and systems.

Living organisms are made up of cells. Some organisms only consist of a single-cell, and others are multicellular and contain lots of cells. There is an order of organisation for these cells.

In order of increasing complexity; 

organelle - cell - tissue - organ - organ system.

Organelle - These are tiny structures within cells. They can only be seen when using a                           powerful microscope as they are so small. They are cell structures that are                             specialised  to carry out a particular function or job. 

Cell -  Cells are also specialised to carry out a particular function, so their structures can                vary. An example of this are the red blood cells found in humans, that are specialised             in carrying oxygen.

Tissue -  A tissue is a group of cells with similar structures that work together to perfom a                     specific function. A group of tissues that also works together to perform a specific                 function would be an organ.

Organ - An organ is a group of tissues that work together to perform a function. An example              of an organ would be leaves on plants or lungs in mammals. 

Organ System - Group of organs with related functions. Organs work together in organ                                    systems, and each system does a different job. An example of an organ                               system is the digestive system that can be found in mammals. The digestive                          system is made up of organs such as; the stomach, intestines, pancreas and                         liver.

b) Cell structure

2.2 describe cell structures, including the nucleus, cytoplasm, cell membrane,

cell wall, chloroplast and vacuole

2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall,

chloroplast and vacuole

Animal and plant cells have certain structures in common, these are; 

Nucleus: an organelle which contains genetic material that controls it's activities. It is surrounded by the cell membrane. 

Cytoplasm: this is a gel-like substance where most of the cell's chemical reactions happen. It contains enzymes, which control these reactions. 

Cell membrane: this forms the outer surface of the cell and controls the substances that go in and out. 

Plant cells also have additional structures that they do not share with animal cells; 

Cell wall: This is a hard structure made of cellulose that surrounds the cell membrane. It supports the cell and strengthens it. 

Chloroplast: It is here that photosynthesis happens, which makes food for the plant. Chloroplasts contain a green substance called chlorophyll, which is used in photosynthesis. 

Vacuole - Both plant and animal cells can have these, however they are never permanent in animal cells, but they always are in plant cells. It is a large organelle that contains cell sap, which is a weak solution of sugars and salts that help to support the cell. 

2.4 compare the structures of plant and animal cells.

Differences between the two; 

• Plant cells have additional structures in their cells that animal cells do not. 
• These include: chloroplasts, cell wall, and vacuole. 
• However, some animal cells do have a vacuole, but these are never permanent like they are in plant cells.

Similarities between the two;

• Both have nuclei.
• Both have cytoplasm.
• Both have a cell membrane.

The Nature and Variety of Living Organisms (Section 1)

Characteristics of Living Organisms (Section 1a)

1.1 Understand that living organisms share the following characteristics: 

• they require nutrition 
• they respire 
• they excrete their waste 
• they respond to their surroundings 
• they move 
• they control their internal conditions 
• they reproduce 
• they grow and develop. 

All living organisms share the same eight basic characteristics. They must have all of these characteristics in order to count as being a living organism, and to therefore count as being alive. 

• They require nutrition. 

All living organisms need nutrients to provide them with energy for growth and tissue repair. These nutrients required from food include; fats, protein, vitamins, minerals and carbohydrates.

• They respire 

The process in which organisms release energy from their food.Nutrient molecules are broken down in chemical reactions, releasing energy.

• They excrete their waste 

Removal of toxic materials from the body. Waste products like carbon dioxide have to be removed from the body and this is done through a process known as excretion. 

• They respond to their surroundings 

Living organisms react to changes in their surroundings. An example of this is the way in which plants can grow towards a light source if light is scarce in the environment. 

• They move 

Living organisms move towards and away from things. 

• They can control their internal conditions (homeostasis)

This is the ability to control their internal conditions, such as temperature and water content, and keep this at the level needed in order for them to survive and function. 

• They reproduce 

Living organisms produce offspring and this allows for their species to survive. 

• They grow and develop

Living organisms grow and develop until they reach their adult form. 

The best way to remember these characteristics is through the acronym: Mrs Gren. 

Movement 

Respiration

Sensitivity

Growth

Reproduction

Excretion

Nutrition

The only characteristic not included in this acronym is homeostasis, the ability to control internal conditions. 

b) Variety of living organisms 

1.2 describe the common features shared by organisms within the following 
main groups: plants, animals, fungi, bacteria, protoctists and viruses, and 
for each group describe examples and their features as follows (details of life 

cycle and economic importance are not required)

Plants;

• Multicellular
• They have chloroplasts (can photosynthesise) 
• Their cells have cell walls (made of cellulose)
• Store carbohydrates as sucrose or starch. 
• Examples include; flowering plants like cereals (maize) and herbaceous legumes (peas and beans)

Maize.

Animals; 

• Multicellular
• Don't have chloroplasts (cannot photosynthesise)
• Their cells do not have cell walls.
• Most have nervous coordination. Can respond rapidly to changes in their environment. 
• They can usually move around from one place to another.
• Often store carbohydrates in the form of glycogen. 
• Examples; mammals and insects.

                                                       Typical housefly.

Fungi;

• Some are single-celled
• Others have body called mycelium (made up of thread like structures,) contain lots of nuclei. 
• They cannot photosynthesise.
• Their cell walls have cell walls (made of chitin.)
• Most are saprotrophic feeders.
• Can store carbohydrates as glycogen. 
• Examples; years and mucor.

Different examples of fungi. 

Protoctists; 

• Single-celled
• Microscopic
• Some have chloroplasts, similar to plant cells. 
• Others are closer to animal cells. 
• Examples: chlorella (plant-cell like) and amoeba (animal-cell like, lives in pond water.)

Chlorella

Bacteria:

• Also single-celled and microscopic.
• Do not have a nucleus.
• Have a circular chromosome of DNA.
• Only some can photosynthesise. 
• Most bacteria feed off other organisms, both living and dead. 
• Examples: Pneumoccoccus and Lactobacillus bulgaricus.

Diagram of cross-section of typical bacterium.

Viruses: 

• These are particles, not cells. 
• Smaller than bacteria. 
• Can only reproduce inside living cells.
• Organisms that rely on other organisms in order to survive = parasites. 
• They infect all types of living organisms. 
• Come in varying different shapes and sizes. 
• Have no cellular structure, have protein coat around genetic material. 
• Examples: HIV, influenza virus, tobacco mosaic virus. (Stops tobacco leaves from producing chloroplasts, discolours them.)

                                     Diagram of cross-section of typical flu virus. 

1.3 recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria,

protoctists or viruses.

Pathogens are organisms that cause disease.They come in many different forms, including some; fungi, protoctists, bacteria and viruses. For example, plasmodium is a protoctist that causes malaria and influenza virus is a virus that causes flu and HIV.