Viruses

Characteristics

• Infectious agent

• Non-cellular

• Tiny – 30,000 in single file across one millimetre on average

• Obligate intracellular parasites

• No metabolic activity external to their host cell

• Multiply only within their host cell

• No enzyme activity if not in contact with the host cell

• Organic: composed of hereditary material (DNA or RNA) is surrounded by a protein coat

• Hereditary material replicated and transcribed within host cell

• Living or non-living?

Structure 

Textbook Diagram: look at the outline structure of virus.

Textbook Diagram: look at the variety of virus shapes.

Economic Importance 

• Cause disease of Livestock and Animal Pets: foot and mouth, rabies

• Crop Diseases: mosaic disease of tobacco, potato and tomato

Medical Importance

• Human Diseases: common cold, measles, AIDS, flu, measles, chicken pox, hepatitis

• Cancer: some cancers are caused by viruses

Uses of Viruses

• Vaccine: cowpox used against smallpox

• Genetic Engineering: viruses are used to insert ‘foreign’ DNA into the target cell’s DNA

• Biological Control: keep rabbit population in check

Reproduction of Viruses 

• Attachment: the virus comes in contact with the host cell and sticks to its surface

• Penetration: the viral hereditary material or the entire virus enters the host cell

• Replication: the viral hereditary material is released from the protein, the viral hereditary material redirects the host cell’s metabolism to make many copies of the viral hereditary material and viral proteins

• Assembly: viral hereditary material and proteins come together forming new viruses

• Release: new viruses pass to the outside by bursting of host cell or by ‘budding’

Most viruses cannot survive for long outside their host cell.

Transfer to host cells is purely by chance – viruses do not actively search for new host cells.

Antibiotics do not have any effect on viruses.

Amoeba - A member of the Protoctista (Protista)  

Amoeba Characteristics

• Unicellular, eukaryote, no cell wall.

• Reproduction: binary fission.

• Movement: use of pseudopodia.

• Feeding: phagocytosis — similar to our phagocytic white blood cells.

Amoeba Structure

Textbook Diagram: typical structure of an Amoeba cell.

Cytoplasm

• Ectoplasm: jelly-like outer layer of cytoplasm next to the cell membrane. - restricts the entry of water by osmosis - supports and strengthens the cell

• Endoplasm: liquid inner cytoplasm in which the organelles are suspended.

Functions of Some Cell Parts  

Food Vacuoles

• Solid food ingested by phagocytosis is digested in the food vacuoles.

• Products of digestion pass form the food vacuole into the cytoplasm.

• Indigestible material is egested at the cell membrane.

Contractile Vacuole

• Active expulsion of the excess water that enters Amoeba by osmosis.

• Maintains cytoplasm at the correct concentration — osmoregulation.

Pseudopods

• Temporary narrow extensions of the cell for locomotion and food capture.

• Amoeba makes movement responses to external stimuli such as light and chemicals.

Flowering Plant Structure

External Structure of Flowering Plant

Textbook Diagram: external structure of a young flowering plant.

• Root: the underground portion of the plant that develops form the radicle of the plant embryo.

• Tap Root: long, large main root that develops from the radicle of the plant embryo.

• Fibrous Roots: set of many similar size roots emerging from the base of the stem.

• Adventitious Roots: roots that develop from stem nodes.

• Shoot: the aerial parts of a flowering plant that develop from the plumule of the plant embryo, stems, buds, flowers and leaves.

• Branch: a side stem that developed from an axillary bud.

• Leaf: an expanded outgrowth of a stem; main ‘food factory’ of the plant.

• Petiole: leaf stalk — not always present.

• Midrib and Veins: transport and strengthening tissue for leaf.

• Lamina: broad, thin, flat part of leaf — often called ‘blade’ of the leaf.

• Node: the point of origin of a leaf on a stem.

• Internode: the section of stem between two successive internodes.

• Axil: the angle between the upper side of a leaf and its stem.

• Axillary Bud: will develop into a side branch or flower.

• Terminal Bud: increase in length of the stem forming new leaves and axillary buds.

• Flower: terminal bud modified for sexual reproduction.

• Fruit: ‘fertilised ovary’ protecting and dispersing the seeds.

• Lenticels: loose open cork tissue for gas exchange for efficient aerobic respiration.

Functions of Plant Parts

Function of Roots

• Anchors plant in soil.

• Absorption of water and mineral nutrients.

• Vegetative reproduction e.g. root tubers of orchid and dahlia.

• Food storage e.g. taproot of carrot, turnip or sugar beet.

Function of Stems

• Formation of buds, leaves and flowers.

• Supports leaves in good light conditions to maximise photosynthesis.

• Vegetative reproduction e.g. stem tuber of potato

• Food storage e.g. stem tuber of potato.

Function of Leaves

• Photosynthesis.

• Transpiration at leaves ‘pulls water up the plant’.

• Vegetative reproduction e.g. plantlets on Bryophyllum leaf margins.

• Food storage e.g. thick fleshy leaves of onion bulb and cabbage.