Biology revision

Cell Ultrastructure: Plant vs. Animal Cells

1. Plant Cells

   • Cell wall, mitochondrion, chloroplast, cell membrane, cytoplasm, vacuole, nucleus, and ribosome.

2. Animal Cells

   • Mitochondrion, cell membrane, cytoplasm, nucleus, and ribosome.

   • Note: Animal cells lack cell walls, chloroplasts, and large permanent vacuoles.

Cell Ultrastructure: Fungal vs. Bacterial Cells

1. Fungal Cells

   • Cell wall, mitochondrion, cell membrane, cytoplasm, vacuole, nucleus, and ribosome.

2. Bacterial Cells

   • Cell wall, cell membrane, ribosome, and plasmid.

   • Note: Bacterial cells lack a nucleus and membrane-bound organelles.

Cell Wall Composition

• Plant Cells: Made of cellulose.
• Fungal and Bacterial Cells: Made of different chemical materials (not cellulose).

Diffusion

The movement of molecules down a concentration gradient from a higher to a lower concentration. It is a form of passive transport and does not require energy.

Osmosis

The movement of water molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane.

Osmotic Effects on Cells

1. Animal Cells
   • Can burst (in high water concentration) or shrink (in low water concentration).
2. Plant Cells
   • Can become turgid (swollen/firm) or plasmolysed (membrane pulls away from wall).

Active Transport

The movement of molecules and ions against a concentration gradient. This process requires energy (ATP) for membrane proteins to move the substances.

DNA Base Pairing Rule

DNA is a double-stranded helix held by complementary base pairs:

• Adenine (A) always pairs with Thymine (T).
• Cytosine (C) always pairs with Guanine (G).

Messenger RNA (mRNA)

A molecule that carries a complementary copy of the genetic code from the DNA in the nucleus to a ribosome, where proteins are assembled from amino acids.

Functions of Proteins

• Structural components
• Enzymes (biological catalysts)
• Hormones (chemical messengers)
• Antibodies (defense)
• Receptors (signaling)

Enzyme Vocabulary

• Active Site: The part of the enzyme complementary in shape to a specific substrate.
• Degradation Reaction: Converts one substrate into multiple products.
• Synthesis Reaction: Converts multiple substrates into one product.

Enzyme Activity and Denaturation

Enzymes are most active in optimum conditions (specific temperature and pH). High temperatures or extreme pH can denature the enzyme, changing the shape of the active site and stopping the reaction.

Stages of Genetic Engineering

1. Identify and extract the required gene from the source chromosome.
2. Extract the plasmid from a bacterial cell.
3. Insert the required gene into the bacterial plasmid using enzymes.
4. Insert the modified plasmid into a host bacterial cell to create a GM organism.

Aerobic Respiration

Occurs when oxygen is present. Glucose is broken down into pyruvate (2 ATP), which then enters the mitochondria to produce carbon dioxide, water, and a large number of ATP molecules.

• \text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy}

Fermentation Pathways

Occurs in the absence of oxygen, yielding only 2 ATP per glucose molecule:

• Animal Cells: \text{Glucose} \rightarrow \text{Lactate} + \text{Energy}
• Plant and Yeast Cells: \text{Glucose} \rightarrow \text{Carbon Dioxide} + \text{Ethanol} + \text{Energy}

Locations of ATP Generation

• Stage 1 (Glycolysis): Always occurs in the cytoplasm.
• Fermentation: Completed in the cytoplasm.
• Aerobic Respiration: Completed in the mitochondria.