Characteristics of life
1. Excretion – Many chemical reactions take place inside the cells of an organism in order to keep it alive. Some of these chemical reactions result in that poisonous substances (CO2) and waste substances (urea) get produced. Excretion removes: these poisonous/waste substances for example urea, which is a waste substance of protein degradation. It contains Nitrogen (N). Excretion also removes the excess water and salts taken in with the diet and spent hormones. The kidneys then excrete all these as a watery solution called urine.
1. Reproduction – production of new individuals (offspring are produced). Single-cell organisms (protoctista or bacteria) use division, which means that the cell simply divides into two and each new cell, becomes an independent organism.
Multi-cellular organisms (Asexually): In some complex organisms, part of the body may grow and develop into a separate individual. For example, a small piece of steam planted in the soil may form roots and grow into a complete plant.
Asexual reproduction in animals: Some species of invertebrate animals are able to reproduce asexually and one example is Hydra which is a small animal of which is 5-10 mm long and lives in ponds attached to pondweed.
Multi-cellular organisms (Sexually): Sexual reproduction involves the production of sex cells. These sex cells are called gametes and they are made in reproductive organs. The process of cell division, which produces the gametes, is called meiosis. In sexual reproduction, the male and female gametes come together and fuse which means that their cytoplasm and nuclei join together to form a single-cell called a zygote. The zygote then grows into a new individual.
1. Respiration – Most of the processes taking place in cells need energy to make them happen. For example: Building up proteins from amino acids or making starch from glucose needs energy. Respiration is the process by which energy is produced from food. Respiration is chemical reactions, which takes place in cells. There are two different kinds of respiration.
– Aerobic respiration (cellular respiration): which means that oxygen (O2) is needed for this particular chemical reaction, which takes place in the mitochondria. The food molecules all contain carbon, hydrogen and oxygen atoms. The whole process is called oxidation and the food is said to be oxidized.
The aerobic respiration can be summed up by the equation:
C6H12O6 (aq) + 602 (g) ——-> 6CO2 (g) + 6H2O (l) +2830 kJ
We inhale O2 from the air and exhale CO2. This is called gaseous exchange.
Anaerobic respiration: The word anaerobic means “the absence of oxygen”. In this process, energy is still released from food by breaking it down chemically but the reactions do not use oxygen though they often produce carbon dioxide.
1. Growth – Most single-celled (unicellular) creatures increase in size. Multi-cellular creatures start of as single cell organisms; however increase in the number of cells in their bodies by cell division (mitosis) produces an organism made up thousands or millions of cells, which means that they increase in size. As time goes these organisms also become more complicated (the new cells become specialized and form tissues and organs). These organisms also eventually change their shape. Also read the answer what happens to carbohydrates during cellular respiration
1. Nutrition – There are two principle methods of obtaining food and these are called autotrophic and heterotrophic nutrition.
Autotrophic organisms (autotrophs) build up all the organic molecules they need from simple inorganic substances. For example plants are autotrophs. They build up large, complex molecules (carbohydrates, proteins and lipids) from small inorganic molecules (carbon dioxide, water and mineral salts) by photosynthesis. Plants, blue-green bacteria and algae uses this metod to produce food
Heterotrophic organisms (heterotrophs) use readymade organic compounds as their food source. The heterotrophs digest the organic compounds to simpler substances and absorb the products into their body. Examples of heterotrophs are Animals, fungi and some bacteria and protoctista. Animals take in food, in the form of complex organic molecules (carbohydrates, proteins and lipids) and digest them to simpler compounds (glucose and amino acids), which can be absorbed.
Fungi also digest their food source, which usually is dead and decaying matter but do so by a process of external digestion. They often release digestive enzymes into their food and absorb the soluble products back into their bodies. They are called saprotrophs.
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