Year 9 Biology Revision Notes

Key Features:
- Single-celled
- Microscopic
- No nucleus
- DNA is Circular
- Have the following components:
- Cell wall
- Cell membrane
- Cytoplasm
- Plasmids
Metabolic Processes:
- Some species perform photosynthesis.
- Most obtain nutrients by feeding on living or dead organisms.
Examples:
- Lactobacillus bulgaricus (used to make yogurt)
- Pneumococcus (causes pneumonia)
Important Note: Prokaryotes are categorized as simple cells.

Characteristics:
- These organisms possess a nucleus.
Major Groups of Eukaryotic Organisms:
1. Plants
- Features:
  - Multicellular
  - Contain chloroplasts for photosynthesis.
  - Cell walls made of cellulose.
  - Store carbohydrates as starch and sucrose.
- Examples:
  - Maize, peas, beans
1. Animals
- Features:
  - Multicellular
  - No chloroplasts
  - No cell walls
  - Capable of movement
  - Have nervous coordination
  - Store carbohydrates as glycogen
- Examples:
  - Humans, insects
1. Fungi
- Features:
  - Multicellular (some are single-celled)
  - No chloroplasts
  - No cell wall
  - Feed by extracellular digestion
  - Body is composed of hyphae forming a mycelium
  - Cell walls made of chitin
- Examples:
  - Mucor, yeast
1. Protoctists
- Features:
  - Usually single-celled
  - Some exhibit characteristics of plants, while others resemble animals
- Examples:
  - Amoeba, Chlorella, Plasmodium (causes malaria)

Graph Analysis: Enzyme activity vs. temperature shows various stages:
- A to C: Reaction speed increases as temperature increases.
- C to E: Enzyme begins to denature, leading to decreased activity.
Important Notes:
- At very low temperatures, enzyme activity is minimal.
- Enzymes have an optimum temperature for maximum activity. For humans, this temperature is about 37°C.
- If temperature becomes too high, the enzyme denatures, causing the active site to change shape, and therefore, the reaction stops.

Definition of Optimum pH:
- Each enzyme has a specific pH at which its activity is maximized.
Denaturation:
- If the pH becomes too acidic or alkaline, the enzyme denatures.
- The change in the active site means that the substrate can no longer bind.
Examples of Enzymes:
- Pepsin works best at pH 2 (stomach)
- Amylase functions optimally at pH 7.

Mechanism: The enzyme has a specific shape with a region known as the active site.
A molecule called the substrate fits perfectly into the active site, analogous to a lock and key.
Upon binding, a chemical reaction occurs, resulting in the release of products.

Description:
- A single-celled green algae.
Key Features:
- Has two flagella which are tail-like structures that enable movement (swimming or moving towards light for photosynthesis).

Comparison of Organisms:
- Animals: Multicellular, no cell wall, nucleus present, eat other organisms.
- Plants: Multicellular, have cell walls made of cellulose, perform photosynthesis.
- Bacteria & Protoctists: Mostly unicellular, some may photosynthesize, have cell walls (bacteria made of peptidoglycan).
- Fungi: Multicellular with cell walls made of chitin, feed on dead matter, no chlorophyll.
- Viruses: Not classified as living organisms, require a host cell to replicate, no cellular structure.

Types of Biological Molecules:
- Carbohydrates: Composed primarily of carbon, hydrogen, and oxygen.
- Proteins: Made from amino acids containing carbon, hydrogen, oxygen, and nitrogen.
- Lipids (Fats/Oils): Composed primarily of carbon and hydrogen.

Glucose: Test using Benedict's solution. Positive result shows a color change to orange/red.
Starch: Test using iodine solution. Positive result shows blue-black color.
Proteins: Use Biuret test; positive result shows purple.
Lipids: Test with ethanol to observe a cloudy white layer if positive.

Experiment Design:
- Investigate enzyme activity at different temperatures or pH levels.
- Independent Variable: Temperature or pH
- Dependent Variable: Rate of reaction.
- Control Variables: Amount of enzyme, substrate concentration, and total volume.