01: Cells and the Chemistry of Life

How to observe the Parts of the Cell?

• Light microscopes: magnify objects up to 1000x

• Electron microscopes: magnify objects more than 200 000x

A camera can be fitted to either type of microscope to take pictures, these are called micrographs.

• Light micrographs can come out as colour images

• Electron micrographs are black-and-white images but can be artificially colourized.

Longitudinal cut

• cutting along the length of the cell

Transverse cut

• cutting across the length of the cell

What is a cell?

• A cell is a unit of life consisting of a mass of living matter called: protoplasm.

• There are layers in cells.

Protoplasm

• complex jelly-like substance

• many chemical activities that allow the cell to survive and grow are carried out in the protoplasm

• made up of:

  • cell membrane

  • cytoplasm

  • nucleus

Cell membrane

• made up of lipids and proteins

• is a partially permeable membrane

  • allows only some substances to pass through

• controls the movement of substances in and out of the cell

The cell membrane is made up of a lipid bilayer.

Cell wall

• encloses the entire plant cell

• made up of cellulose

  • protects the cell from injury

  • gives the plant cell a fixed shape

• fully permeable

Cytoplasm

• jelly-like substance

• enclosed by the cell membrane

• where most cell activities occur

• contains organelles

  • a cellular structure that performs a specific job within a cell

Nucleus

• surrounded by a membrane: nuclear membrane

• contains genetic information in the form of chromosomes

Function:

• controls cell activities:

  • cell growth

  • repair of worn-out parts

• essential for cell division

Cells without a nucleus are unable to divide, thus, have a shorter life span.

Chromatin

• each chromosome is a long thread-like structure (46 chromosomes)

• made up of proteins and a compound called deoxyribonucleic acid or DNA

  • hereditary information is stored in DNA

  • carries instructions that a cell needs for carrying out its activities

• during cell division,

  • chromosomes condense and shorten to become thick, rod-shaped structures

Nuclear membrane

• separates the contents of the nucleus from the rest of the cytoplasm

Rough Endoplasmic Reticulum (RER)

• consists of a network of flattened spaces line with a membrane

• appears rough when viewed under the electron microscope

  • small particles called ribosomes are attached to its outer surface

  • the outer surface of the RER is continuous with the nuclear membrane

Ribosomes

• small round structures

• either attached to the RER or lie freely

  • ribosomes attached to the RER: make proteins that are transported out the cell

  • ribosomes lying freely: make proteins that are used within the cytoplasm

• synthesises protein in the cell

  • ribosomes attached to the RER make proteins that are used within the cytoplasm

    • ribosomes make proteins by joining amino acids together

The RER transports proteins that are synthesised by the ribosomes to the Golgi body for secretion out of the cell.

Smooth Endoplasmic Reticulum (SER)

• does not have ribosomes attached to its membrane

• SER is more tubular than RER

  • connected to the RER

• synthesises fats and steroids

• converts harmful substances into harmless substances through detoxification

Golgi Body

• shaped like a disc

• consists of a stack of flattened spaces surrounded by membranes

  Vesicles

  • tiny spherical spaces enclosed by a membrane

    • fuses with one side of the Golgi body and pinches off from the opposite side

• chemically modifies substances made by the ER

• stores and packages these substances in vesicles for secretion out of the cell

Process of How Substances Made By The ER are Moved Out of The cell:

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

2. These vesicles then fuse 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)

• small oval or sausage-shaped

• releases energy via aerobic respiration (oxidises food to release energy for cellular activities)

  • food substances are broken down to release energy

  • used by the cell to perform cell activities such as growth and reproduction

Aerobic Respiration Formula:

glucose + oxygen ———> carbon dioxide + water

Chloroplasts

• oval structures found in plant cells

• contain a green pigment called chlorophyll (converts light energy to make glucose)

• chlorophyll is essential for photosynthesis

*Chloroplast is bigger than mitochondrion

Photosynthesis Equation/Formula:

carbon dioxide + water ———> glucose + oxygen

Vacuoles

• fluid-filled space enclosed by a partially permeable membrane

• stores substances

  Plant cells:

  • large central vacuole

    • contain a liquid called cell sap

      • contains dissolved substances eg. sugars, mineral salts and amino acids

  Animal cells:

  • many small vacuoles

    • contain water and food substances

    • exist temporarily

Differentiation

• when cells develop special structures or lose certain structures to carry out specific functions

  • by which a cell becomes a specialised cell for a specific function

Specialised Cells:

1. Red Blood Cells

   • contains haemoglobin which binds to oxygen and transports it around the body

   • has a circular, biconcave shape which increases the surface area-to-volume ratio so that oxygen can diffuse in and out at a higher rate

   • lacks a nucleus to store more haemoglobin for transport of oxygen

   • flexible to squeeze through capillaries easily

2. Muscle Cells

   • elongated and cylindrical to contain many nuclei (cell division) and mitochondria

   • mitochondria to provide the energy (aerobic respiration) for the contraction of the muscle cell

3. Root Hair Cells

   • long and narrow root hair (elongated structure) to increase the surface area-to-volume ratio to absorb water and mineral salts at a higher rate

   • more mitochondria to release energy for active transport

   • cell sap has low water potential for active transport for mineral salts and healthy growth of the plant