Structures and functions in living organisms. Revision Notes

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Structures and functions in living organisms

2.1 Describe the levels of organisation within organisms:

Organelles -> Cells -> Tissues -> Organs -> Organ Systems.

Smallest ------------------------------------------->Largest

2.2 Recognise 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

Nucleus – The largest organelle in the cytoplasm. This controls the cell. It contains chromosomes which carry genes.

Cytoplasm – The living material that makes up a cell. It is made up of many structures called organelles.

Cell Membrane – This is a thin layer on the surface of the cell. It is a partially permeable membrane between the cytoplasm and the outside as it controls which substances pass in either direction.

Cell Wall – This is a layer found outside the cell membrane. It is freely permeable so anything can pass through it. It is responsible to maintain Plant Turgor (the plant’s shape)

Chloroplast – These absorb light energy to make food in the process of photosynthesis

Vacuole – This is filled with cell sap, a store of dissolved sugar and solutes to provide energy for the plant, until it can create its own.

2.4 Describe the differences between plant and animal cells.

Plant cells have a cell wall to maintain plant Turgor, whereas animal cells do not have this

Plant cells have chloroplasts in order to carry out photosynthesis, whereas animals do not have this

Plant cells have a large permanent vacuole, whereas plant cells do not have this.

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

Carbohydrates - Carbon, Hydrogen, Oxygen

Proteins - Carbon, Hydrogen, Oxygen, Nitrogen (Sulphur in two amino acids)

Lipids - Carbon, Hydrogen, Oxygen

2.6 Describe the structure of carbohydrates, proteins and lipids

They are large molecules made up from smaller basic units:

Carbohydrate (starch and glycogen) are made up of simple sugars such as glucose

Proteins are made up of amino acids

Lipids are made up of fatty acids and glycerol

2.7 Describe the tests for glucose and starch


Benedict’s Solution (pale blue) is added to a prepared sample and heated to around 95o, if the colour of Benedict’s solution changes to green, yellow or orange-red, a significant amount of glucose is present


Iodine solution (light brown) is added to a sample, id the iodine changes colour to black, starch is present.

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

Metabolic Reaction - The chemical reactions that cause the life processes of organisms to occur

Biological Catalyst - A catalyst that speeds up metabolic reactions

  • Enzymes help cells carry out all the life processes quickly. Without them, these metabolic reactions would happen too slowly for life to carry on.
  • Enzymes are specific and only work with their specific substrate.
  • Carbohydrases are enzymes which digest starch
  • Proteases are enzymes which digest proteins
  • Lipases are enzymes which digest lipids

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

  • Enzymes work best at their optimum temperature.
  • At low temperatures, molecules do not have energy and move around too slowly to catalyse a reaction
  • At high temperatures, the structure of the active site will change and become denatured

2.10 Understand how the functioning of enzymes can be affected by changes in pH

  • Enzymes work best at their optimum pH
  • Very high or very low pH could slow down the rate of action by the enzyme and even denature them

2.11 Describe how to carry out simple controlled experiments to illustrate how enzyme activity can be affected by changes in temperature.

  • Developed black and white negative film has a gelatine layer on it, which can be digested by proteases.
  • Put five strips of film in protease solution of 10oC, 20oC, 30oC, 40oC, 50oC
  • Note how long it takes for the gelatine to be digested and the film to be transparent.

2.12 Recall simple definitions of diffusion, osmosis and active transport

Diffusion - The net movement of molecules along a concentration gradient; it is a passive process and does not use any energy. e.g. Oxygen from alveoli into red blood cells

Osmosis - The movement of water molecules through a partially permeable membrane, from a higher water potential to lower water potential e.g. cell crenation/ cell lysis

Active Transport - The movement of molecules from an area of low concentration to an area of high concentration, up a concentration gradient using energy. e.g. villi absorb soluble nutrients during digestion even when there is no concentration gradient.

2.13 Understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

Cells have a partially permeable membrane across which small molecules can transport themselves across either via active transport, osmosis or diffusion.

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

 If a plant is place in a solution of low water potential, water will move via osmosis out of the cytoplasm of the plant cells, but the cell will not crenate, because of the cell wall which is turgid and prevents the plant from becoming flaccid.

Similarly, if a plant is placed in pure water, water will move via osmosis in to plant cells, but the cells will not lyce and will not burst because the turgid cell wall prevents this.

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: A high surface area to volume ratio leads to a higher rate of movement in and out of cells because the membrane which particles can cross will be larger

Concentration Gradient: The steeper the concentration gradient, the faster the rate of movement

Temperature: A high temperature means that particles have more kinetic energy so are likely to bump into the cell membrane more times and with more energy, passing through to the other side

2.16 Describe simple experiments on diffusion and osmosis using living and non-living systems

Osmosis: Attach visking tubing to a glass tube and put starch solution into this tubing. Put this system in a beaker of water and watch how the liquid level in the glass tubing rises.

Diffusion: Same kind of experiment. Put glucose and starch solution in visking tubing and suspend in water. After a few hours, do a glucose and starch test for the surrounding water and find that glucose has diffused and starch has not.

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

Photosynthesis - The process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.

Photosynthesis transforms light energy into chemical energy in the bonds in glucose.

2.18 recall the word equation and the balanced chemical symbol equation for photosynthesis


Carbon Dioxide + Water ----------------> Glucose + Oxygen



6CO2 + 6H2O ----------------> C6H12O6 + 6O2


2.19 understand how carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis

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CO2 Concentration, Light intensity and temperature are limiting factors of photosynthesis.

For light intensity, it is proportional to the rate of photosynthesis up to a point. During this time, light intensity is the limiting factor. After this point, even if light intensity increases further, rate of photosynthesis will not be affected as something else is the limiting factor. The same is true for CO2 concentration.

For temperature, an increase in temperature will result in an increase in the rate of photosynthesis up to a point (25-30oC). After this point, the rate of photosynthesis will drop rapidly as enzymes required for the ...

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