Cell Structure and Function
Using the light microscope the following structures of cells can be seen. Animal and plant cells have an encircling cell membrane, cytoplasm, nucleus. Animal cells do not have a cell wall, chloroplasts or a large central vacuole of cell sap but plant cells do.
Using an electron microscope many new structures and details become visible — mitochondria, greater detail of chloroplast structure, ribosomes, nuclear envelope, nucleolus and pores plus an outline of the structure of cell membranes.
Cell Membrane Fluid-mosaic structure involving a bi-lipid layer with proteins. The membrane is semi permeable, keeps cell contents together, controls entry and exit of materials and by active transport specific materials are moved across it.
Cytoplasm: Sticky fluid of water, sugars, salts and other solutes in which the organelles are suspended, many biochemical processes take place here, e.g., glycolysis and fermentation.Nucleus: Contains the hereditary material, DNA — deoxyribonucleic acid, visible as chromatin in active cells and condensed into chromosomes when the nucleus is dividing.
Nucleolus: Inside the nucleus. Made from RNA. Produces mRNA for protein synthesis.
Mitochondria: The aerobic steps of respiration occur here — Krebs cycle in the matrix or lumen and the electron transport system in the cristae,
Ribosomes: Made of RNA and protein; specific proteins are made by the ribosomes under ‘instructions’ from the mRNA sent from nucleus.
Chloroplast: Photosynthesis occurs here — light phase in the chlorophyll-rich grana, dark phase in stroma.
Large plant cell vacuole: Storage of water, food, waste and assists in the elongation of cells during growth. Provides turgor pressure hich inflates cell and gives it strength.
Cellulose cell wall of plants: Protects and supports plant cell. The middle lamella of pectin glues neighbouring plant cell walls together.
Eukaryote and Prokaryote cells
Prokaryotic cells: These are cells that do not have a nucleus – their genetic material, DNA, is not contained within a nuclear membrane. Prokaryotic cells do not have membrane-bound organelles such as mitochondria or chloroplasts. All organisms with prokaryotic cells are placed in the Kingdom Monera i.e. the bacteria.
Eukaryotic cells: The presence of a nucleus identifies the cell as a eukaryotic cell. Membrane-bound organelles such as mitochondria and chloroplasts are only present in eukaryotic cells. Members of the other four kingdoms (Protista, Fungi, Plants and Animals) are eukaryotic organisms.
Tissues, Organs and Systems
A tissue is a group of similar specialised cells such as nerve or muscle tissue in animals and xylem or phloem in plants.
An organ consists of a number of tissues working together to form a specialised part of an organisms system eg heart, lungs, flower and leaf. Organ systems have a number of specialised organs working together such as the digestive or circulatory systems.
Practical Activities
Practical activity 1) Be familiar with and use the light microscope.
Cells are small, so microscopes are needed to see them. The coverslip placed over the specimen on the slide gives a clearer view by reducing the scattering of light as it passes through the slide.The magnification is calculated by multiplying the power of the objective lens by the power of the eyepiece:
Practical activity 2: Prepare and examine one animal cell and one plant cell (e.g. own cheek cells and onion cells) unstained and stained using the light microscope (x100, x400)
