¶ Learning Outcomes:
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Identify cell structures (including organelles) of typical plant and animal cells from diagrams, photomicrographs and as seen under the light microscope using prepared slides and fresh material treated with an appropriate temporary staining technique:
- chloroplasts
- cell surface membrane
- cell wall
- cytoplasm
- cell vacuoles (large, sap-filled in plant cells, small, temporary in animal cells)
- nucleus
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Identify the following membrane systems and organelles from diagrams and electron micrographs:
endoplasmic reticulum- mitochondria
- Golgi body
- ribosomes
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State the functions of the membrane systems and organelles identified above
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Compare the structure of typical animal and plant cells
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State, in simple terms, the relationship between cell function and cell structure for the following:
- absorption – root hair cells
- conduction and support – xylem vessels
- transport of oxygen – red blood cells
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Differentiate cell, tissue, organ and organ system
¶ 1. What are cells?
- Cells are the basic building blocks of life
- They are the simplest structural and functional units of life
¶ 2. How do we study cells?
- Cells are studied with the help of
- Light microscopes (that magnify objects up to 1,000 times) and
- Electron microscopes (that magnify objects up to 200,000 times)
- A section of a cell can be viewed under the microscope in by cutting a cell:
- Along the length of the cell, the longitudinal section
- Across at right angles the length of the cell, the transverse section
¶ 3a. What cellular components can you observe under the light microscope?
- The plasma membrane, cytoplasm, nucleus, vacuole are observable under in both animal and plant cells under the light microscope
- In plants, the chloroplast and cell wall is also visible
¶ 3b. What cellular components can you observe under the electron microscope?
- Animal Cell:
- Plant Cell:
- Click here to see more electron micrographs by H. Jastrow
¶ 4. Protoplasm
- Is the living material in a cell, which is made up of:
- Cell surface membrane
- Cytoplasm
- Nucleus
¶ 5a. Cell Wall
- Found in plant cells, but absent in animal cells
- Encloses the entire plant cell surrounding the plasma membrane
- Fully permeable (does not control substances entering or leaving the cell)
- Made up of cellulose
- Making the cell wall rigid but flexible
- Protecting the cell from injury
- Giving the cell a regular shape
¶ 5b. Cell Surface Membrane / Plasma Membrane
- Is the membrane that surrounds the cytoplasm of the cell
- Made up of lipids and proteins
- Separates the cellular contents from the surrounding environment
- Partially/selectively permeable (NOT “Semi-permeable”)
- Controls the movement of substances in and out of the cell (allowing certain substances to pass through but not others)
¶ 5c. Cell Surface Membrane / Plasma Membrane
- A jelly-like substance that fills the inside of the cell and is enclosed by the plasma membrane that contains
- Dissolved nutrients (proteins, sugars, etc.)
- Organelles (cellular structures that are specialised to perform a specific function within a cell)
- Site where most cellular activities and chemical reactions occur
- *Cytosol refers to the fluid only (excluding the organelles)
¶ 5d. Nucleus
- Spherical shaped; usually the largest structure in the animal cell
- Surrounded by the nuclear membrane/envelope
- Contains hereditary genetic information in the form of deoxyribonucleic acid (DNA)
- DNA are packaged with proteins to form chromosomes
- Each human cell contains 46 (23 pairs) of chromosomes
- Controls cellular activities (e.g. cell growth and repair of worm-out parts)
- Essential for cellular division
- Essential for cellular division
¶ 5e. Rough Endoplasmic Reticulum
- Consist of a network of flattened spaces lined with a membrane
- Ribosomes are attached outer surface, making the surface appear rough when viewed under the electron microscope
- The outer surface of the RER is continuous with the nuclear envelope
- The RER transports proteins made by ribosomes to the Golgi body for secretion out of the cell
¶ 5f. Ribosomes
- Small round structures that are attached to membrane of the RER or lie freely in the cytoplasm
- Needed to synthesis proteins in the cell
- Ribosomes attached to the RER make proteins that are usually transported out of the cell
- Ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of the cell
¶ 5g. Smooth Endoplasmic Reticulum
- Tubular sacs that do not have ribosomes attached to its membrane
- Synthesis fats and steroids
- Converts harmful substances into substances by detoxification
¶ 5h. Golgi body / Golgi apparatus
- Consists of a stack of membrane-bound sacs that are shaped like a disc
- Vesicles can be seen fusing with one side of the Golgi body and pinching 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
- Secretory pathway in a cell:
- Vesicles containing substances made by the ER pinch off from the ER.
- Vesicles fuse with the Golgi body releasing the substances made by the ER which may be modified.
- Secretory vesicles containing modified substances pinch off from the Golgi body and move towards the plasma membrane.
- Secretory vesicles fuse with the cell membrane and their contents exit the cell.
¶ 5i. Mitochondrion
- Plural: Mitochondria
- Oval/sausage-shaped organelle
- Site of aerobic respiration, whereby food is oxidised to release energy for cellular activities
- Not visible under light microscope; requires electron microscope to be seen
¶ 5j. Chloroplast
- Oval structure found in plants
- Contains chlorophyll which is required for photosynthesis to occur
- Not all plant cells have chloroplasts
¶ 5k. Vacuole
- Fluid filled space enclosed by a partially permeable membrane
- Animal cells typically have numerous small temporary vacuoles that store water and food temporarily
- Plant cells typically have one large permanent central vacuole containing sugars, minerals and amino acids, that help in maintaining turgor pressure against cell wall
¶ 6. Animal vs Plant Cells
¶ 7. Red Blood Cells
- Transports oxygen from lungs to all parts of the body
- Cytoplasm contains haemoglobin for binding to oxygen for transport around the whole body
- Lacks a nucleus, to allow more haemoglobin to be packed for carrying more oxygen
- Biconcave shape increases surface area to volume ratio for faster diffusion of oxygen into and out of the cell
- Flexible and deformable membrane allows it to squeeze through tiny capillaries
¶ 8. Muscle Cells
- Responsible for body movement
- Contains many mitochondria for aerobic cellular to release energy for contraction of the muscle cell
- Has contractile protein fibres that contract and relax to bring about movement of the muscle
- Has many nuclei to allow for cell division
¶ 9. Root Hair Cells
- Are modified root epidermal cells that aid in absorption of water and mineral salts
- Long and narrow extension to increase surface area to volume ratio for the increased rate of absorption of water and dissolved mineral salts
- Maintenance of a lower water potential in vacuole allows water to root hair cell by osmosis
- Large number of mitochondria to release energy for active transport of dissolved mineral salts