Year 9 Biology

1. Cell Structure and Function

Animal vs. Plant Cells

Organelle

Function

Found in?

Nucleus

Controls cell activities, contains DNA

Animal & Plant

Cytoplasm

Jelly-like substance where chemical reactions happen

Animal & Plant

Cell Membrane

Controls what enters and exits the cell

Animal & Plant

Mitochondria

Site of respiration, produces energy (ATP)

Animal & Plant

Ribosomes

Make proteins

Animal & Plant

Cell Wall

Provides structure and support (made of cellulose)

Plant Only

Chloroplasts

Contain chlorophyll for photosynthesis

Plant Only

Vacuole

Stores cell sap (water, nutrients, and waste)

Plant Only

2. Types of Cells

  • Eukaryotic Cells (Have a nucleus, e.g., animal and plant cells).

  • Prokaryotic Cells (No nucleus, e.g., bacteria).

    • DNA is in a loop (plasmid) instead of a nucleus.

    • Smaller than eukaryotic cells.

3. Specialized Cells

Cell Type

Adaptation

Function

Red Blood Cell

No nucleus, biconcave shape

Carries oxygen

Nerve Cell (Neuron)

Long, branched

Transmits electrical signals

Muscle Cell

Many mitochondria

Provides movement

Root Hair Cell

Large surface area

Absorbs water and minerals

Sperm Cell

Tail for movement, many mitochondria

Fertilizes egg

Palisade Cell

Many chloroplasts

Photosynthesis

4. Microscopy

Types of Microscopes

  1. Light Microscope

    • Uses light to magnify images.

    • Can view live specimens.

    • Lower magnification and resolution.

  2. Electron Microscope

    • Uses electron beams for high detail.

    • Much higher magnification and resolution.

    • Can’t view live specimens.

Key Microscopy Calculations

  • Magnification Formula: Magnification = Image Size/Actual Size

  • Units:

    • 1 mm = 1000 µm (micrometers)

    • 1 µm = 1000 nm (nanometers)

How to Use a Microscope

  1. Place the slide on the stage.

  2. Select the lowest objective lens.

  3. Use the coarse focus knob to adjust.

  4. Fine-tune with the fine focus knob.

  5. Change to a higher objective lens for more detail.

5. Cell Division (Mitosis)

  • Mitosis is cell division for growth and repair.

  • Produces two identical daughter cells.

  • Stages of Mitosis:

    1. Interphase: DNA is copied.

    2. Prophase: Chromosomes become visible.

    3. Metaphase: Chromosomes line up in the middle.

    4. Anaphase: Chromosomes are pulled apart.

    5. Telophase: Two nuclei form.

    6. Cytokinesis: A cell splits into two.

6. Meiosis (Cell Division for Reproduction)

  • Meiosis is the process of cell division that produces gametes (sperm and egg cells).

  • Produces four genetically different haploid cells (each with half the chromosomes).

Stages of Meiosis

  1. Interphase - DNA is copied.

  2. Meiosis I (First Division)

    • Prophase I - Chromosomes pair up and exchange DNA (crossing over).

    • Metaphase I - Chromosome pairs line up in the middle.

    • Anaphase I - Chromosomes are pulled apart.

    • Telophase I - Two new nuclei form.

  3. Meiosis II (Second Division)

    • Prophase II - New spindles form.

    • Metaphase II - Chromosomes line up again.

    • Anaphase II - Chromatids are pulled apart.

    • Telophase II & Cytokinesis - Four unique haploid cells form.

Differences Between Mitosis and Meiosis

Feature

Mitosis

Meiosis

Purpose

Growth & Repair

Reproduction

Number of Divisions

1

2

Number of Cells Produced

2

4

Genetic Variation

None (identical cells)

Yes (different cells)

Chromosome Number

Diploid (same as parent)

Haploid (half of parent)