• The aerobic steps of respiration occur here – Krebs Cycle and Electron Transport System.

• 36 Of the 38 atPs from one molecule of glucose are produced in the mitochondrion.

• Liver, muscle and nerve cells are rich in mitochondria.

• Bone and fat cells have low numbers of mitochondria.

• Root hair cells and meristematic cells of plants have large numbers of mitochondria.

• Stem and root ground tissue cells of plants are low in mitochondria.

Textbook Diagram: detail of mitochondria structure - for recognition purposes only.

Ribosomes:

• Composed of RNA and protein.

• Function in protein synthesis – translation of mRNA into a specific sequence of amino acids.

Chloroplast

• Photosynthesis is the major function of the chloroplast.

• The light stage takes place in the green internal membranes.

• The dark stage occurs in liquid part of the chloroplast.

• Starch may be stored in the chloroplast

Textbook Diagram: detail of chloroplast structure - for recognition purposes only. Large Plant Cell Vacuole

• Storage of water, food (sugar, amino acids), ions, wastes.

• Role in cell elongation during plant growth.

Plant Cell Wall

• Composed of cellulose.

• Permeable to water and solutes

• Protects and supports plant cells.

• Prevents plant cells bursting in more dilute solutions.

• The middle lamella of pectin glues neighbouring plant cell walls together.

• Structural role – it is the ‘plant skeleton’.

Prokaryotic Cell: no nucleus. Prokaryotic cells do not have membrane-bound organelles such as nuclei, mitochondria or chloroplasts. All prokaryotes are placed in the Kingdom Monera i.e. the bacteria.

Eukaryotic Cell: membrane-bound nucleus is present. Membrane-bound organelles such as nuclei, mitochondria and chloroplasts are only present in eukaryotic cells. The Protista, Fungi, Plants and Animals are eukaryotic organisms.

Enzymes  

Proteins that function as biological catalysts are called enzymes.

Enzymes speed up specific metabolic reactions.

Low contamination, low temperature and fast metabolism are only possible with enzymes.

Metabolism is fast, with the product made to a high degree of purity.

General Properties  

• Catalysts

• Protein

• Specific

• Reversible — can catalyse the reaction in both directions

• Denatured by high temperature and change in pH

• Rate of action affected by temperature and pH

Protein Nature of Enzymes

• Composed of C, H, O and N. Sulphur (S) may also be present.

• One or more polypetide chains - large number of linked amino acids.

• Formed by the ribosomes – translation of mRNA during protein synthesis.

• Denatured by high temperature and unfavourable pH.

Folded Shape of Enzymes

• The polypeptide chains are folded into a particular three-dimensional shape.

• The correct folded shape is essential for enzyme action.

• The shape gives the enzyme special domains that function as active sites.

• The compatible substrate molecules bind to the active site.

• Different enzymes have a differently shaped active site.

Roles of Enzymes in Plants and Animals Enzymes catalyse all metabolic reactions.

• Lower the activation energy – the energy input needed to bring about the reaction.

• Regulate the thousands of different metabolic reactions in a cell and in the organism.

• The activity of a cell is determined by which enzymes are active in the cell at that time.

• Cell activity is altered by removing specific enzymes and/or synthesising new enzymes.