1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS 

Active transport 

• The movement of particles against the concentration gradient (from an area of lower concentration to an area of higher concentration) using energy released during respiration

eg: 

1. Higher concentration of nutrients in blood, lower concentration in gut 
2. Active transport - against diffusion/osmosis - against concentration gradient
3. Allows nutrients to be taken into blood 
4. Needs energy from respiration 

Things that affect movement of substances - 

1. Surface to area volume ratio -(larger surface area to smaller volume ratio = substances move in/out faster) 
2. Temperature -(warmer = more energy, move faster substances move in/out faster) 
3. Concentration gradient -(big difference in concentration = substance move faster) - doesn't affect active transport

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

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
• Partially permeable membrane - small holes in it (only small molecules - eg: water can get through), eg: cell membrane 
• Water molecules pass both ways during osmosis (move randomly) 
• Steady net flow of water into region with fewer water molecules 
• Other solution gets more dilute 

Osmosis in cells - 

• Water moves in and out of cells by osmosis 
• Tissue fluid (water, with oxygen, glucose etc. dissolved in it) surrounds cells in body. Squeezed out of blood capillaries to supply cells 
• Tissue fluid has different concentration to fluid inside cell - water will move into/out of cell by osmosis (to/from tissue fluid) 

Turgid cells - 

• Turgid - when the cells in a plant are all hydrated (plump and swollen) 
• Hydrated plant - all cells draw in water by osmosis = plump and swollen (turgid)  
• Contents of cell push against cell wall - turgor pressure - helps support plant tissues 
• Dehydrated plant - cells lose water, lose turgor pressure - cells become flaccid (plant wilts) 
• Plant doesn't completely lose shape - inelastic cell well keeps it supported

Osmosis experiments - 

1. Living system - potato cylinders 

• Cut potato into equal cylinders, measure and record lengths
• Put cylinders in beakers with different sugar solutions (eg: pure water, different levels of concentrated sugar solution, very concentrated sugar solution) 
• Leave in beaker for at least half an hour 
• Take out cylinders - measure and record 
• Drawn in water (osmosis) = will be longer 
• Water drawn out = slightly smaller 

2. Non-living system - visking tubing 

• Tie wire around 1 end of visking tubing, put glass tube in other end, tie visking tubing around it 
• Pour sugar solution down glass tube into visking tubing 
• Measure where sugar solution comes up to in glass tube 
• Put in beaker of pure water 
• Leave overnight 
• Measure liquid in glass tube again 
• Water drawn in by osmosis - level in glass tube higher

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

Diffusion

• The gradual movement of particles from a high concentration to a lower concentration 
• Happens in liquids and gases - particles free to move about 
• eg: perfume in air

Cell membranes -

• Hold cell together and control substances entering/exiting 
• Substances move in and out of cells by osmosis, diffusion and active transport 
• Only small molecules can dissolve through (eg: glucose, amino acids, water, oxygen) 
• Large molecules (eg: starch, proteins etc.) can't diffuse through cell membranes  

Diffusion experiment (non-living system) - 
- Phenolphthalein - pH indicator, pink in alkaline, colourless in acidic solution

1. Make agar jelly with phenolphthalein and dilute sodium hydroxide (jelly will be pink) 
2. Fill beaker with dilute hydrochloric acid 
3. Use a scalpel to cut out cubes of jelly - put them in the beaker (use different size cubes and a timer to investigate surface area and diffusion)
4. leave cubes - turn colourless (acid diffuses into agar jelly, neutralises sodium hydroxide)

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS 

Enzymes 

• Catalysts produced by living things - biological catalysts
• Catalyst - a substance which increases the speed of a reaction without being changed or used up in the process 
• Allows individual reactions to be sped up (without raising temperature and speeding up unwanted reactions too/damaging cells) - reduce the need for high body temperatures
• Only have enzymes to speed up useful chemical reactions (metabolic reactions) 
• All proteins (chains of amino acids) 

Specificity -

• Substrate - molecule changed in a reaction 
• An enzyme molecule has an active site (where a substrate then joins on) 
• Suited to one particular reaction - needs correct substrate to fit into active site 
• Lock and key model: 

Temperature - 

• Changing temperature changes rate of an enzyme-catalysed reaction 
• Higher temperature increases reaction rate at first (more heat - particles have more energy, higher collision rate) 
• Lower temperatures slow reaction down - lower collision rate 
• Denaturing - If the enzyme gets too hot, some of the bonds break and the shape of the active site changes (substrate doesn't fit anymore). Reaction eventually stops once all enzymes are denatured. It's irreversible. 
• Optimum temperature - reaction is at its fastest just before it gets too hot and denatured. (eg: most important enzymes in humans have an optimum temperature of 37 degrees) 

Effect of temperature on enzyme activity - 

How fast a product appears: 
-Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen 

• Collect oxygen given off - how much in a set time? 
• Use a water bath - how does temperature affect amount of product produced/activity level of catalase? 
• Control any variables (eg: enzyme concentration, pH, volume of solution etc.) 

How fast a substrate disappears: 
-Amylase catalyses breakdown of starch to maltose 

• Use iodine to test for starch (iodine solution turns from brown/orange to blue/black) 
• Time how long it takes for starch to disappear (sample starch solution regularly) - compare 
• Use water bath - how does temperature affect activity of amylase? 
• Control all variables

pH - 

• Affects enzymes 
• Too high/low - interferes with bonds in enzyme, can cause it to become denatured 
• Optimum pH - (generally pH7), pH at which the rate of reaction is the fastest 
• eg: pepsin (breaks down proteins in stomach), optimum pH = pH 2

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

The Kingdoms - 


Plants - 

• Multicellular 
• Have chloroplasts - they photosynthesise 
• Cells have cell walls (made of cellulose) 
• Store carbohydrates as sucrose or starch 
• eg: cereals (maize etc.), herbaceous legumes (peas, beans etc.)

Animals - 

• Multicellular 
• No chloroplasts 
• No cell walls 
• Most have a form of nervous coordination (respond quickly to changes in environment) 
• Usually can move around 
• Often store carbohydrates as glycogen 
• eg: mammals (humans etc.), insects (houseflies, mosquitos etc.)

Fungi - 

• Some are single-celled, other have body called a mycelium (made up of hyphae - thread-like structures, contain lots of nuclei) 
• Can't photosynthesise 
• Cells have cell walls (made of chitin) 
• Most feed by saprotrophic nutrition (secrete extracellular enzymes - dissolve the food - absorb nutrients) 
• Store carbohydrates as glycogen 
• eg: yeast (single-celled fungus), nucor (multicellular, mycelium and hyphae) 

Protoctists - 

• Single-celled 
• Microscopic 
• Some have chloroplasts (
• Some are similar to plant cells, others more like animal cells 
• eg: chlorella (plant cell-like), amoeba (animal cell-like, live in pond water) 

Bacteria (prokaryotes) - 

• Single-celled 
• Microscopic 
• No nucleus 
• Have a circular chromosome of DNA 
• Some photosynthesise
• Most feed off other organisms 
• eg: lactobacillus bulgaricus (used to make milk go sour to make yoghurt, rod shaped), pneumococcus (spherical shape) 

Viruses - 

• Particles, not cells 
• Smaller than bacteria
• Only reproduce inside living cells (parasitic) 
• Infect all types of living organisms 
• Different shapes and sizes 
• No cellular structure - protein coat around some genetic material (DNA or RNA) 
• eg: influenza virus, tobacco mosaic virus (makes the leaves of tobacco plants stop producing chloroplasts - discoloured), HIV 

Pathogens - cause disease 
eg:

• Protoctist - Plasmodium, causes malaria 
• Bacterium - Pneumococcus, cause pneumonia 
• Viruses - Influenze virus, causes flu 
• Viruses - HIV, causes AIDS 

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

Levels of organisation - 

1. Similar cells -> tissues 
2. Tissues -> organs 
3. Organs -> organ systems 

1. Similar cells are organised into tissues 

• Tissue - group of similar cells that work together to carry out a particular function 
• eg: plants - xylem tissue (transporting water and mineral salts) and phloem tissue (transporting sucrose and amino acids) 
• Can contain more than one cell type 

2. Tissues are organised into organs 

• Organ - group of different tissues that work together to perform a function 
• eg: lungs in mammals, leaves (both made up of different tissue types) 

3. Organs make up organ systems 

• Each system does different job 
• eg: digestive system - stomach, intestines, pancreas, liver 

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS

Cells - 

Animal cells - 
- Nucleus - contains genetic material and chromosomes
                 control's cells activities
                 surrounded by its own membrane
- Cell membrane - outer surface of the cell
                           controls substances that enter/exit
- Cytoplasm - gel-like substance
                     where most of the chemical reactions happen
                     enzymes to control reactions
- Mitochondria - carry out some of the respiration reactions
                        most energy from respiration is released here

Plant cells - 
- Nucleus - contains genetic material and chromosomes
                 control's cells activities
                 surrounded by its own membrane
- Cell membrane - outer surface of the cell
                           controls substances that enter/exit
- Cytoplasm - gel-like substance
                     where most of the chemical reactions happen
                     enzymes to control reactions
- Mitochondria - carry out some of the respiration reactions
                        most energy from respiration is released here
- Chloroplasts - where photosynthesis takes place
                       contain chlorophyll
- Cell wall - rigid structure made of cellulose
                 surrounds cell membrane
                 supports and strengthens cell
                 freely permeable
- Vacuole - contains cell sap (weak solution of sugars and salts)
                 supports cell
                 permanent  

Specialised cells - specialised to carry out particular functions, eg: red blood cells (carrying oxygen), white blood cells (defending against disease)  

1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS 

Characteristics of Living Organisms - 

1. Movement - eg: towards food, away from predators
2. Reproduction - for species to survive
3. Sensitivity - reacting to changes in their surroundings
4. Nutrition - energy, growth and repair, eg: proteins, fats, carbohydrates, vitamins, minerals
5. Excretion - waste products removed, eg: carbon dioxide, urine
6. Respiration - releases energy from food
7. Growth - developing