Structures and Functions in Living Organisms


Characteristics of Living Organisms

  • Nutrition - provides energy and raw materials for growth and repair
  • Growth  - developing into adult form
  • Reproduce - produce offspring in order for species to survive
  • Respire - release energy from food
  • Respond - react to changes in surroundings
  • Move - towards food and water, away from predators and poisons
  • Excrete - get rid of waste: carbon dioxide, urine
  • Control - internal conditions: temperature and water content.
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Animals Cells

Plant Cells

Animal and Plant Cells

Nucleus - contains genetic material and controls the cells activities

Cell Membrane - controls what substances go in and out of the cell

Cytoplasm- jelly-like substance where chemical reactions take place

Chloroplasts - photosynthesis takes place and also contains chlorophyll

Cell Wall - supports the cell

Vacuole - Stores Sap

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  • Multicellular 
  • Photosynthesise
  • Cell walls are made from cellulose
  • Stores carbohydrates as sucrose or starch.

Examples: Peas, Cereals (Maize)

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  • Multicellular
  • Don't photosynthesis
  • No cell walls
  • Respond to changes
  • Easily move around
  • Store carbohydrates as glycogen

Examples: Mammals (humans), Insects (mosquitoes) 

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  • Single celled
  • Can't photosynthesise
  • Cell wall is made from chitiin
  • Secrete enymes to dissolve food so nutrients are absorbed
  • Store carbohydrates are glycogen

Examples: Yeast

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  • Single celled
  • Contain chloroplasts

Examples: Chlorella, Amoeba

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  • Single celled
  • No nucleus
  • Circular chromosome of DNA
  • Feeds off of organisms (dead or alive)

Examples: Lactobaccillus, Pneunococcus

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  • Made from particles
  • Reproduce inside living cells
  • Can by any shape and size

Example: HIV, Influenza Virus

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Living things produce enzymes which act as catalysts. A catalyst increases the speed of reaction without being changed or used up.

Every enzyme has an active site where a substrate (a mole changed in the reaction) joins onto the enzyme. 

To change the rate of reaction, change the temperature.

A high temperature will increase the rate as heat gives the particles energy therefore they will move more meaning there is a higher collison rate.

A low temperature will decrease the rate as the particles will not have energy and therefore move less. This meaning that there is a low collision rate and a slower reaction will take place. 

HOWEVER, if the temperature is TOO HOT then the bonds between the enzymes break so the active site will no longer fit and the reaction stops. When this happens the enzyme is denatured as it cannot function.

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Diffusion is the movemnt of particles from an area of a higher concentration to an area of  a lower concentration. 

Diffusion occurs in liquids and gases as the particles are free to move randomly.

Small molecules, like glucose, are able to diffuse through the cell membranes of a cell.

Large molecules however, like starch, are too big and therefore unable to diffuse.

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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.

A cell membrane is partially permeable because more water particles are on one side and so there is a steady net flow of water into the region containing less. E.g. sucrose solution will become more dilute. 

If a cell is short of water, the solution inside becomes concentrated where the outside is more dilute. 

Plants draw water in by osmosis and look swollen, they have become turgid. The contents will push against the cell wall which helps to support the plant tissues. 

If a plant has no water then the plant begins to wilt as the cells lose pressure and become flaccid. 

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Diffusion Experiment

Non-living system

  • First, make agarjelly with phenolphthanlein and dilute sodium hydroxide - where the jelly will turn pink.
  • Fill a beaker with dilute hydrochloric acid. Using a scalpel, cut pieces out of the jelly and put into the beaker. 
  • Leave the cubes in the beaker where eventually they will go colourlesss because the acid has diffused into the jelly and neutralised the sodium hyrdoxide. 
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Osmosis Experiments

Living System - Potato Cylinders

  • Cut up potato into identitcal cyclinders and get two beakers with different sugar solutions in - one should have pure water and the other concentrated sugar solution
  • Measure the lengths of the cylinders of potato and leave in beaker. Take out after an hour and measure again. If the cylinders take in water, they become longer. 

Non Living - Visking Tubing

  • Tie a wire around an end of visking tubing and put a glass tube in the other end. 
  • Pour sugar solution down glass tube into the visking tubing and then place the visking tubing in a beaker of pure water, measuring where the sugar solution comes up to.
  • Leave tubing over night and measure liquid the next day. The water will be taken into the visking tubing by osmosis, forcing the liquid to rise up the glass. 
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Active Transport

Active Transport- the movement of particles against a concentration gradient (an area of lower concentration to an area of higher concentration) using energy released during respiration. 

When the gut contains a high concentration of nutrients, they naturally diffuse into the blood. Active Transport on the other hand allows the nutrients to be absorbed into the blood despite the concentration gradient. 

Factors Affecting the Movments of Substances

  • Surface Area to Volume Ratio - the rate is higher in cells with a larger surface area to volume ratio.
  • Temperature - as particles get warmer they have more energy to move faster. So when temperture rises the substances move in and out quicker. 
  • Concentration gradient - substances move faster if there is a greater difference in concentration. 
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