Chapter 1: Cell Structure and Organisation

What is a cell?

• A cell is a unit of life. It consists of a mass of living matter called protoplasm

What does a protoplasm consist of?

• The protoplasm consists of the cell membrane, cytoplasm and nucleus

Cell membrane

• Partially permeable membrane that controls substances entering or leaving the cell

Cell wall

• Fully permeable

• Protects the cell from injury, gives the plant cell a fixed shape

Cytoplasm

• Jelly-like substance

• Contains organelles

• Site where cell activities occur

What are the parts of the cytoplasm?

• Nucleus

• Rough endoplasmic reticulum

• Ribosomes

• Golgi body

• Mitochondria

• Chloroplasts

• Vacuoles

Nucleus

• Controls cell activities such as cell growth and repair of worn-out parts

• Essential for cell division

• Contains DNA (in the form of chromatin)

Rough endoplasmic reticulum (RER)

• Studded with ribosomes

• Synthesises proteins and transports them to the Golgi Body for secretion out of the cell

Ribosomes

• Attached to RER: Synthesises proteins that are transported out of the cell

• In cytoplasm: Synthesises proteins that are to be used within the cell

Smooth Endoplasmic Reticulum

• Synthesises fats and steroids

• Converts harmful substances into harmless substances via detoxification

Golgi body (Golgi apparatus)

• Chemically modifies substances made by the RER

• Stores and packages these substances into vesicles for secretion out of the cell

How are substances made by the ER moved out of the cell?

1. Vesicles transport substances within the cell. Small vesicles containing substances made by the ER are pinched off from the ER.

2. These vesicles then fused with the Golgi body and release their contents into the Golgi body. The substances made by the ER may be modified inside the Golgi body.

3. Secretory vesicles containing these modified substances are pinched off from the Golgi body. They then move to the cell membrane.

4. The secretory vesicles fuse with the cell membrane and their contents are released out of the cell.

Mitochondria, singular: mitochondrion

• Site of aerobic respiration, where food substances like glucose is broken down to release energy for cell activities (growth and reproduction)

Chloroplast

• Found in plant cells

• Contains chlorophyll which converts light energy to chemical energy for the formation of glucose during photosynthesis

Vacuole

Store substances within the cell

Plants: Large central vacuole, contains sugars, mineral salts and amino acids

Animals: Many small vacuole, contains water and food

What is differentiation?

• Differentiation is the process by which a cell become specialised for a specific function

Specialised cells

• Red blood cell

• Muscle cell

• Root hair cell

Red blood cell

• Contains haemoglobin which binds to oxygen and transport it round the body.

• Circular and biconcave shape to increase surface area to volume ratio so that oxygen can diffuse in and out at a faster rate.

• No nucleus to enable cell to store more haemoglobin for oxygen transport

• Is flexible and can squeeze through capillaries easily

Muscle cell

• Is elongated and cylindrical in shape, contains many nuclei and mitochondria

• Many mitochondria to supply energy for contraction of muscles

Root hair cell

• Long and narrow protrusion increases surface area to volume ratio for faster absorption of water by osmosis and mineral salts by diffusion and active transport from soil solution

• Cell contains many mitochondria which releases energy during respiration needed to transport mineral salts from the soil solution into the root hair cell by active transport

What organelle is different in plant cell and animal cell?

• Cell wall

• Chloroplast

• Vacuole

Tissue

• Tissue is a group of similar cell working together to perform a specific function

Organ

• Organ is a structure made up of different tissues working together for a specific function