Ohne Titel

The Nature and Variety of Living Organisms

1.1 Characteristics of living organisms

Movement

• Movement is an action by an organism or part of an organism causing a change of position or place.
• For example, climbing plants move their tendrils (growths from their stems) around fixed objects so that they can climb walls

Respiration

• Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism (chemical reactions in cells).
• For example, when a human eats an apple, the sugars in the apple are broken down to release energy.

Sensitivity

• Sensitivity is the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.
• For example, a deer detects movement in the nearby grass and runs away from a potential predator.

Growth

• Growth is a permanent increase in size and dry mass (without including the water in the organism) by an increase in cell number or cell size or both.
• For example, a puppy will grow very rapidly in its first few months and will never return to its original tiny size.

Reproduction

• Reproduction is the processes that make more of the same kind of organism.
• For example, bacterial cells can split in two to make two bacterial cells.

Excretion

• Excretion is the removal from organisms of waste products from metabolism, toxic materials, and substances which are in excess of requirements.
• For example, oxygen is a waste product made by plants, and it leaves the plant through its leaves.

Nutrition

• Nutrition is the taking in of materials for energy, growth and development.
• For example, plants take in light, water and carbon dioxide, and animals need organic compounds and water.

Control

• Organisms are in control of their internal environments.
• Keeping internal conditions (such as temperature) the same is known as homeostasis.

1.2-1.4 Variety of living organisms

Eukaryotic cells

• Eukaryotic cells are found in plants, animals, fungi and Protoctista (single-celled organisms that don’t fit other categories).
• They are 10-100 micrometres in size.
• A eukaryote is an organism made up of eukaryotic cells.

Prokaryotic cells

• They are 0.1 - 5.0 micrometres in size.
• A prokaryote is an organism made up of prokaryotic cells.
• Bacteria are prokaryotes.

Animals

• Animal cells have no cell wall and no chloroplasts (so do not carry out photosynthesis).
• Animals are multicellular (made of many cells) and they don't make their own food, but they store carbohydrates as glycogen.
• They often have nervous coordination (using nerves) and are able to move around.
• Mammals (like whales) and insects (like mosquitoes) are examples.

Plants

• Plant cells are surrounded by cell walls (made of a substance called cellulose) and contain chloroplasts (carry out photosynthesis).
• Plants are multicellular (many cells) and they make their own carbohydrate food, which they store as sucrose or starch.
• Plants can be divided into flowering and non-flowering plants.
  • Flowering plants include cereals (e.g. maize) and herbaceous legumes (e.g. peas).
  • Non-flowering plants include pines and ferns.

Fungi

• Fungi cells have cell walls (that contain a substance called chitin) and no chloroplasts.
• Fungi can be multicellular or unicellular and they are saprotrophic (they feed by secreting digestive enzymes and absorbing broken down decaying matter), and often store carbohydrates as glycogen.
• Their bodies are made up of mycelium, which contains many thread-like structures called hyphae.
• Mushrooms and single-celled yeast are examples.
• Fungal cells are similar to plant cells, apart from:
  • There are no chloroplasts in fungal cells.
  • The cell walls of fungal cells are made from chitin instead of cellulose.
• Fungi can be unicellular or multicellular and are made up of hyphae (thread-like structures).
• The hyphae are able to grow and penetrate tissues, such as human skin or the surface of plants.
• Athlete's foot is caused by fungi.

Bacteria

• Bacteria are unicellular and they have cell walls and circular loops of DNA (which is not inside a nucleus).
• Some bacteria photosynthesise, and some feed off decaying matter.
• Bacteria can be rod-shaped (like Lactobacillus which turns milk into yoghurt) or spherical (like Pneumococcus which causes pneumonia).
• Prokaryotic cells may have one or more small rings of DNA, which are called plasmids.
• These plasmids can replicate (have copies made) and move between cells so that genetic information can be shared.
• Prokaryotic cells do not contain mitochondria (where respiration takes place) or chloroplasts (where photosynthesis takes place).
• Prokaryotic cells do not have a nucleus (where DNA is stored).
• Instead, their genetic material is stored in a single DNA loop in the cytoplasm (watery jelly that fills the cell).
• Bacteria are small living cells that either damage cells directly or by producing toxins (poisons).

Protoctista

• Protoctista are unicellular, and their cells have nuclei (membrane-bound structures that contain the cell's genetic materials).
• Some, like Amoeba, are similar to animal cells. Some, like Chlorella, are like plant cells and have chloroplasts.
• Protoctista are single-celled eukaryotic organisms (they have a nucleus).
• They are often transferred to the host organism by a vector, such as an insect or mosquito.
• Plasmodium is a Protoctist, spread by mosquitoes, that causes malaria.

Viruses

• Viruses are surrounded by a layer of protein, which forms a ‘protein coat’.
• Viruses have genetic material (either DNA or RNA) that contains the instructions for the building and functioning of the virus.
• Viruses are tiny, non-living (do not contain cells) particles that can reproduce rapidly within any other living organism.
• An example of a plant virus is tobacco mosaic virus.
• Examples of human viruses are HIV and the flu virus.