2 - Structure & Functions in Living Organisms

(a) Level of Organisation

The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently. Cells are often called the "building blocks of life”.

• Organelles - Cell structure specialised with a specific function

• Cells - Basic functional & structural units in a living organism

• Tissues - Groups of cells of the similar structure carrying out the same function

• Organs - Made from different tissues working together to perform specific functions

• Organ Systems - Groups of organs working together to carry out body functions

(b) Cell Structure

Both animal & plant cells have:

• Cell Membrane –  you can imagine this as a balloon filled with water (actually cytoplasm) which contains everything else. The cells are not flat. Its main function is to control what goes in and out.

• Cytoplasm – is what the cell is full of and is where chemical reactions happen.

• Nucleus – The control centre or brain, controls what the cell does and contains the DNA which is the blueprint for reproduction

• Mitochondria - releases the most energy in respiration, sometimes called the powerhouse of the cell.

• Ribosomes -  this is where protein is synthesised.

But only plant cells have:

• Cell Wall – Primarily structural, remember plants do not have a skeleton to keep them rigid and upright.

• Vacuole – has numerous functions. It can contain waste, store water, isolate harmful substances and keep the pressure of the cell at the correct level. This can be called turgor. This helps maintain the structure of the tissues of the organism and keeps the cell acid inside.

• Chloroplasts – plants use photosynthesis to feed, animals do not. More of this later but essentially they absorb light from the sun and convert the energy in the sunlight into chemical energy in the form of carbohydrates.

Cell Differentiation

• Specialised cells are those which have developed certain characteristics in order to perform particular functions

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• • Cells specialise by undergoing differentiation: a process that involves the cell gaining new structures within the cell in order for it to be suited to its function

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• • Cells can either differentiate once early on or have the ability to differentiate their whole lives (these are called stem cells)

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• • In animals, most cells only differentiate once, but in plants, many cells retain the ability

Stem Cells

• Many tissues in the human body contain a small number of undifferentiated cells

• These are called stem cells and their function is to divide and produce newly differentiated cells within the tissue for growth and repair

• Adult stem cells from bone marrow are quite useful in medicine as they can be directed to differentiate into several different cell types (unlike adult stem cells from other tissues which can only differentiate into related cell types)

• Stem cells are also found in great numbers in embryonic tissue as there is a large amount of development and differentiation going on during foetal development

• Scientists can clone these embryonic stem cells and direct them to differentiate into almost any cell type

(c) Biological Molecules

There are 3 main types of organic molecule.

Carbohydrate

Protein

Lipid

Which as you probably know is pretty much all we eat, Lipids being the fats and oils.

Carbohydrates

They are made of Carbon, Oxygen and Hydrogen. 

Glucose is sugar and sugar is energy.

There are:

- 6 carbon atoms

- 12 hydrogen atoms

- 6 oxygen atoms

One sugar molecule - monosaccharide

Two sugar molecules joined together - disaccharide

Many sugar molecules joined together - polysaccharide.

Proteins

They are composed of Carbon, Oxygen, Hydrogen and Nitrogen and follow less repetitive patterns, hence becoming so complicated.

Protein molecules are much more complicated.

Proteins are made up of strings of simpler amino acids

Lipids

Lipids are made of Hydrogen, Carbon and Oxygen, but with much less oxygen than in glucose.

Differences can be seen between saturated and unsaturated fats.

Lipids are formed from smaller blocks of fatty acids and glycerol

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