Mudando a forma de aprender

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

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

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.

Sem título