Characteristics of living organisms

Characteristics of living organisms

Look at Figure 1.

Answer these questions 1 List three different living things which you can see in Figure 1. 2 List five different nonliving things which you can see in Figure 1. Characteristics of living things There are seven activities which make organisms different from nonliving things. These are the seven characteristics of living organisms. 1] Movement: All living things move. It is very obvious that a leopard moves but what about the thorn tree it sits in? Plants too move in various different ways. The movement may be so slow that it is very difficult to see. 2] Respiration:Respiration is the release of energy from food substances in all living cells. Living things break down food within their cells to release energy for carrying out the following processes. 3] Sensitivity: All living things are able to sense and respond to stimuli around them such as light, temperature, water, gravity and chemical substances. 4] Growth:Growth is seen in all living things. It involves using food to produce new cells. The permanent increase in cell number and size is called growth. 5] Reproduction:All living organisms have the ability to produce offspring of their own kind. 6] Excretion:All living things excrete. As a result of the many chemical reactions occurring in cells, they have to get rid of waste products which might poison the cells. Excretion is defined as the removal of toxic materials, the waste products of metabolism and substances in excess from the body of an organism.

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7] Nutrition: Living things take in materials from their surroundings that they use for growth or to provide energy. Nutrition is the process by which organisms obtain energy and raw materials from nutrients such as proteins, carbohydrates and fats.

Questions 1] Some yeast, sugar and water are mixed in a testtube. The diagrams show the testtube at the start and after one hour.

Figure 2 a] Which process causes this change? A growth B irritability C reproduction D respiration b] Excretion, irritability and reproduction are characteristics of: A all animals and plants B animals only C plants only D some animals and some plants only c] Which one of the following functions is carried out by green plants but not by animals? A excretion B growth C photosynthesis D respiration d] Figure 3 shows how fish react when the glass on one side of an aquarium tank is tapped with a finger.

What characteristics of living organisms does this demonstrate? A excretion and movement B excretion and nutrition C growth and irritability D irritability and movement 2] Complete the passage below by choosing the words from this list: excretion growth irritability movement nutrition organisms reproduction respiration A] Living things are often called ______________. B] All living things release energy from their food in a process called ______________, which happens inside their cells. C] Some of the energy is used for ________________, which usually happens more quickly in animals than in plants. D] The food from which the energy is released is taken into the body in a process called ________________.

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E] All living things get bigger as they get older. This process is called __________________. F] The production of young is called ____________________. G] Waste substances are removed from organisms by the process of ____________________. H] The seventh characteristic shown by all living organisms is ____________________, which means that they are sensitive to things around them.

Classification of living organisms

Classification can be defined as grouping organisms according to their structural similarities. This means that organisms that share similar features are placed in one group. These groups are arranged from the largest group of organisms to the smallest group of organisms. The groups, from largest to smallest, are arranged as follows: kingdom, phylum (plural phyla), class, order, family, genus (plural genera) and species. The species is the smallest group of organisms. A species can be defined as a group of organisms with similar features, and these organisms are capable of breeding and produce fertile offspring. Horses and donkeys belong to the same kingdom, phylum, class, order, family as well as genus but they are from different species. Therefore, if a donkey and the horse happen to breed, they produce an offspring called a mule. The mule is infertile, meaning that it cannot reproduce offspring because it is a product of organisms of different species. Classification hierarchy has many uses 1] It helps scientists to sort organisms in order. 2] It helps them to identify new organisms by finding out which group they fit. 3] It is easier to study organisms when they are sorted in groups. The hierarchical classification system Classification is traditionally based on studies of morphology(the study of the form, or outward appearance, of organisms) and anatomy(the study of their internal structure, as revealed by dissection).

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There are various sizes of groups into which living organisms are put. The largest group is the kingdom. There are five kingdoms: prokaryotes (which includes bacteria), protoctista, fungi, plants and animals. Each kingdom is further divided into smaller groups called phyla,based on a few features that are shared by some organisms. For example, the arthropod phylum contains all the animals without a backbone that also have jointed legs and a hard covering over their body, such as insects, crustaceans and spiders. A phylum is then subdivided intoclasses, orders, families, genera, and finally species.In this system of classification the various groups are called taxa (singular: taxon). This chart shows the hierarchical system of classification.

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Kingdom

Table 1 shows how this system can be used to classify a human being.

Animalia

all animals, same as zebra

Phylum

Chordata

all animals with a backbone

Class

Mammalian

animals with a backbone, which have hair

Order

Primate

mammals with hands and feet

Family

Hominidae

apes, primitive humans and modern humans

Genus

Homo

primitive humans and modern humans only

Species

sapiens

modern humans only

Scientific name: Homo sapiens Table 1 Classifying the human being

The hierarchical classification system described above is based on two ideas: ? homologous structures ? evolutionary relationships

Homologous structures Homologous structures are features of organisms that are similar in structurebut may look very different from each other and may be used for different purposes. As shown in Figure 2, a horse's front leg, the human arm and a bat's wing are all homologous structures. They have the same number and arrangement of bones and this means that they probably evolved from a single type of structure that was present in a common ancestor millions of years ago. A fly's wing is not homologous with a bat's wing. It may look similar and do the same job but it develops from a completely different origin. The fly's wing has no bones and is not covered by feathers. A bat's wing and a fly's wing are termed analogous.A bat and a fly would not be grouped together!

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Questions A] Each of the vertebrates shown has carpals, metacarpals and phalanges. Name three other bones shared by all three vertebrates.

B] Describe how the metacarpals of the horse differ from those of the human.

C] How do the phalanges of the bat differ from those of the human?

D] Complete these sentences: The human arm, the horse's front leg and the bat's wing are described as ____________________ structures. The wing of the bat and the wing of a fly are described as _____________________ structures.

Classification systems aim to reflect evolutionary relationships By classifying organisms it is also possible to understand evolutionary relationships. Vertebrates all have the presence of a vertebral column, along with a skull protecting a brain, and a pair of jaws (usually with teeth). By studying the anatomy of different groups of vertebrates it is possible to gain an insight into their evolution.

Binomial system of naming species Define and describe the binomial system The binomial system of naming species is an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and the species. Binomial means `two names' the first name gives the genus and the second gives the species. For example, the stoat and weasel are both in the genus Mustela but they are different species the stoat is Mustela ermineaand the weasel is Mustela nivalis.The name of the genus (the generic name) is always given a capital letter and the name of the species (the specific name) always starts with a small letter. Frequently, the specific name is descriptive, for example edulis means `edible', aquatilis means `living in water', bulbosus means `having a bulb', serratus means `having a jagged (serrated) edge'.

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The use of DNA has revolutionized the process of classification. Eukaryotic organisms contain chromosomes made up of strings of genes. The chemical which forms these genes is called DNA. The DNA is made up of a sequence of bases, coding for amino acids and, therefore, proteins. Each species has a distinct number of chromosomes and a unique sequence of bases in its DNA, making it identifiable and distinguishable from other species. This helps particularly when different species are very similar morphologically (in appearance) and anatomically (in internal structure). The process of biological classification called cladistics involves organisms being grouped together according to whether or not they have one or more shared unique characteristics derived from the group's last common ancestor, which are not present in more distant ancestors. Organisms which share a more recent ancestor (and are, therefore, more closely related) have DNA base sequences that are more similar than those that share only a distant ancestor. All living organisms have certain features in common, including the presence of cytoplasm and cell membranes, and DNA as genetic material. All living organisms also contain ribosomes in the cytoplasm, floating freely or attached to membranes called rough endoplasmic reticulum (ER). Ribosomes are responsible for protein synthesis. The five Kingdoms The main groups of living are the 5 kingdoms. They don't include virus since it doesn't obey some characteristics of life. The five kingdoms are: Bacteria, Protoctista, Fungi, Plants, and Animals. 1] The Animal kingdom Animals are multicellular organisms whose cells have no cell walls or chloroplasts. Most animals ingest solid food and digest it internally.



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Arthropods The name arthropod means `jointed limbs', and this is a feature common to them all. They also have a hard, firm external skeleton, called a cuticle, which encloses their bodies. Their bodies are segmented and, between the segments, there are flexible joints which permit movement. In most arthropods, the segments are grouped together to form distinct regions, the head, thorax and abdomen.

1. Crustacea Like all arthropods, crustacea have an exoskeleton and jointed legs. They also have two pairs of antennae which are sensitive to touch and to chemicals, and they have compound eyes. Compound eyes are made up of tens or hundreds of separate lenses with lightsensitive cells beneath. They are able to form a crude image and are very sensitive to movement. Typically, crustacea have a pair of jointed limbs on each segment of the body, but those on the head segments are modified to form antennae or specialised mouthparts for feeding.

2. Insects Insects have segmented bodies with a firm exoskeleton, three pairs of jointed legs, compound eyes and, typically, two pairs of wings. The segments are grouped into distinct head, thorax and abdomen regions. Insects differ from crustacea in having wings, only one pair of antennae and only three pairs of legs. There are no limbs on the abdominal segments. The insects have very successfully colonised the land. One reason for their success is the relative impermeability of their cuticles, which prevents desiccation even in very hot, dry climates.

3. Arachnids Their bodies are divided into two regions, the cephalothorax and the abdomen. They have four pairs of limbs on the cephalothorax, two pedipalps and two chelicerae. The pedipalps are used in reproduction the chelicerae are used to pierce their prey and paralyse it with a poison secreted by a gland at the base. There are usually several pairs of simple eyes.

4. Myriapods They have a head and a segmented body which is not obviously divided into thorax and abdomen. There is a pair of legs on each body segment but in the millipede the abdominal segments are fused in pairs and it looks as if it has two pairs of legs per segment. As the myriapod grows, additional segments are formed. The myriapods have one pair of antennae and simple eyes.

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