Trimestral Bio PDF

The biosphere 1 Life on Earth There is life almost everywhere on Earth, even in the most hostile and extreme environments, such as the ice sheet of Greenland and the Atacama Desert – the driest place on the planet. The biosphere is the sum of all living things on the planet and the physical enviro...

The biosphere 1 Life on Earth There is life almost everywhere on Earth, even in the most hostile and extreme environments, such as the ice sheet of Greenland and the Atacama Desert – the driest place on the planet. The biosphere is the sum of all living things on the planet and the physical environment in which they live. 1.1 How is life on Earth possible? The Earth is unique in the Universe because it is the only planet where life is known to exist. The following factors make life on Earth possible: 2 What makes a living thing ‘living’? Both living and non-living things are made up of matter. However, all living things share certain common characteristics that distinguish them from non-living things. These characteristics can help us identify a mineral as a non-living thing and a butterfly as living. NON-LIVING THINGS Non-living things are made up of inorganic matter. The most abundant chemical elements which make up inorganic matter are: oxygen (O), silicon (Si), aluminium (Al) and iron (Fe). LIVING THINGS All living things, also called organisms, are made up of the same chemical elements. The elements that form part of living matter are known as bioelements. The six most abundant bioelements are: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P) and sulphur (S). They make up more than 90% of living matter. The atoms and molecules of bioelements combine with each other through chemical reactions, producing biomolecules. Biomolecules may be: -​ Inorganic, such as water and mineral salts. -​ Organic (unique to living things), such as carbohydrates, lipids, proteins and nucleic acids. FUNCTION OF BIOMOLECULES Water is where reactions take place in organisms. Carbohydrates provide an energy source for the cells and may also play a structural role. Lipids function as an energy reserve and also contribute to cell structure. Proteins are needed for growth and the maintenance (the process of preserving a condition) of body structures. Nucleic acids are responsible for holding genetic information. 3 Functions of living things The vital functions of nutrition, interaction and reproduction are common to all organisms on Earth despite their incredible diversity. 3.1 Nutrition Nutrition enables organisms to obtain energy to perform activities such as growing and restoring damaged structures. There are two types of nutrition: autotrophic and heterotrophic. AUTOTROPHIC NUTRITION Autotrophic organisms (autotrophs) capture energy from their environment and use it to transform inorganic substances, such as water, carbon dioxide and mineral salts, into organic matter. The process through which most autotrophs make their own food is called photosynthesis. Plants, algae and some bacteria are autotrophs. HETEROTROPHIC NUTRITION Heterotrophic organisms (heterotrophs) cannot produce their own food. They obtain organic matter by feeding on other organisms. Heterotrophs depend on autotrophs and other heterotrophs in order to get the nutrients they need. Animals, protozoans and fungi are heterotrophs. Heterotrophs can: -​ obtain energy from eating plants (herbivores). -​ obtain energy from eating other animals (carnivores). -​ eat both plants and animals (omnivores). -​ obtain nutrients from dead organic matter (saprotrophs) →Fungi are saprotrophic organisms. 3.2 Interaction Interaction is the ability of organisms to obtain information about the changes in their environment and their own organism, and to adapt to these changes. Changes in the environment of an organism, such as changes in temperature and humidity, or in the organism itself, such as hunger, are called stimuli. The adaptations or the reactions to those changes are called responses. Responses can vary considerably. In animals, a response can be a sudden movement of the muscles. In plants, a response can be a slow movement towards the Sun in search of sunlight. 3.3 Reproduction Reproduction is the capacity of organisms to form new individuals similar to themselves. It can be asexual or sexual. ASEXUAL REPRODUCTION Two or more identical individuals are produced from a single one. Cell division in bacteria SEXUAL REPRODUCTION Two individuals of different sexes are required. These organisms produce specialised cells known as gametes. These gametes join together to produce new organisms which are similar, but not identical, to their progenitors. Starfish usually reproduce sexually but some starfish can also reproduce asexually. If a starfish’s arm is cut off and it keeps a part of the centre of the body, a whole new starfish can form from the removed arm. A starfish can also regenerate (to grow after loss or damage) a new arm to replace the lost one. Starfish are able to regenerate lost limbs. 4 Cells: the units of life All living things are composed of one or more cells, each capable of carrying out the functions of life. All cells come from pre-existing cells. According to the number of cells, organisms can be single-celled or multicellular. Single-celled or unicellular organisms, such as bacteria or protozoans, are made up of just one cell. Multicellular organisms, such as human beings, are made up of a large number of cells. 4.1 Types of cells Based on their complexity, there are two types of cells: prokaryotic cells and eukaryotic cells. PROKAROTIC CELLS This is the simplest type of cell. Prokaryotic means ‘before a nucleus’. This is because prokaryotic cells do not have a defined nucleus and the DNA is dispersed in the cytoplasm. This is the cell type found in single-celled organisms such as bacteria. EUKARYOTIC CELLS Eukaryotic literally means ‘with a true nucleus’. In these cells, the genetic material is protected by a double membrane that separates it from the cytoplasm. Eukaryotic cells are more complex than prokaryotic cells because they have specialised organelles. These organelles play different roles in the cell. There are two types of eukaryotic cells: animal cells found in protozoans and animals. plant cells found in algae and plants. Animal cells and plant cells have some organelles in common. They also have their own specific organelles, such as centrosomes in animal cells, and cell walls and chloroplasts in plant cells. These two cell types have three common parts: Cell membrane. A covering (a layer of something that covers something else) which surrounds and protects the cell and controls the passage of substancesin and out of it. Cytoplasm. A viscous liquid which fills the inside of the cell and in which chemical reactions take place. In eukaryotic cells, the cytoplasm contains different types of organelles. Genetic material. This is made up of deoxyribonucleic acid (DNA), which contains the information that directs and controls the functions of the cell. This material also determines an organism’s characteristics and is passed from the parent organisms to their offspring. Parts of a cell