Kingdom Classification | ICSE Class 7 Biology Notes

This note covers the need for classification, the five kingdoms, bacterial shapes and activities, Amoeba and its life processes, mould structure and nutrition, useful and harmful fungi, plant characteristics, vertebrates and the main invertebrate groups.

What is classification, and why do we need it?

Classification means arranging organisms, or living things, into groups according to shared characteristics. A characteristic is a feature used to describe or compare an organism. Classification makes the enormous variety of life easier to study systematically.

A kingdom is a broad group in biological classification. Organisms within a kingdom share important features, although they need not look alike. For example, bread mould and a mushroom have different appearances but both belong to the kingdom Fungi.

Why are shared features useful?

Grouping organisms helps us compare their similarities and differences. It also helps us identify an unfamiliar organism and place it in a suitable group. We can study the important features of a group before examining its individual members.

Appearance alone is not enough. A fungus and a green plant both have supporting cell walls, but they obtain food differently. A cell is the basic structural and functional unit of life. Differences inside cells can therefore be important classification features.

How did the kingdom system change?

The two-kingdom system divided living organisms into Plantae, the plant kingdom, and Animalia, the animal kingdom. It did not adequately separate organisms with different cell structures, numbers of cells or methods of obtaining food. Bacteria and fungi were particularly difficult to place satisfactorily.

R. H. Whittaker proposed the five-kingdom classification in 1969: Monera, Protista, Fungi, Plantae and Animalia. This system uses several important characteristics together. It separates bacteria from organisms with more complex cells and separates fungi from green plants.

Which features distinguish the five kingdoms?

The main bases of five-kingdom classification are cell structure, body organisation, nutrition, reproduction and evolutionary relationships. Nutrition means obtaining food and using it. Reproduction is the production of new individuals. Evolutionary relationships concern how groups are related through changes in living organisms over generations.

What do the cell terms mean?

The nucleus is a cell structure containing genetic material, the information passed from one generation to another. A prokaryotic cell lacks a nucleus enclosed by a nuclear membrane, the membrane surrounding the nucleus. A eukaryotic cell has a membrane-bound nucleus.

Unicellular means made of one cell; multicellular means made of many cells. Body organisation describes how these cells are arranged. A tissue is a group of cells working together; an organ contains tissues performing particular functions.

Autotrophic nutrition means making food from simple substances. Heterotrophic nutrition means depending on other organisms or their products for food. These terms describe methods of nutrition, rather than the size or shape of an organism.

A cell wall is a supporting covering outside the cell membrane, the thin boundary enclosing the cell. Chitin and cellulose are different structural substances found in fungal and plant cell walls respectively. Having a wall does not by itself make an organism a plant.

Note: Classification considers several features together. Yeast is a unicellular fungus, so being single-celled is not, by itself, sufficient reason to identify an organism as a protist.

What are the main characteristics and shapes of bacteria?

Bacteria belong to Monera. Their cells are prokaryotic, so their genetic material is not enclosed within a membrane-bound nucleus. Bacteria occur almost everywhere, including soil, water and other organisms. Some live in extreme environments such as hot springs and deep oceans.

A micro-organism is an organism too small to be seen clearly without magnification. The small size of bacteria does not mean that their activities are unimportant. Different bacteria obtain food in different ways and have very different effects on their surroundings.

How are bacterial shapes named?

The singular names coccus, bacillus and spirillum refer to one bacterium of the corresponding shape. These shape descriptions do not tell us whether a bacterium is useful or harmful. Shape and effect on other organisms are different characteristics.

A spore is a specialised cell or resting form: bacterial spores help survival under unfavourable conditions, whereas fungal spores can develop into new individuals. A flagellum is a long, thin structure used for movement.

The drawing shows groups labelled Cocci, Bacilli, Spirilla and Vibrio. The cocci are rounded, bacilli are rods, spirilla are long and winding, and vibrio are curved. A spore and a flagellum are also labelled.

See Fig. 2.1 in your NCERT textbook

Some bacteria are autotrophic, but the vast majority are heterotrophs. Bacteria reproduce mainly by fission, meaning division. Sometimes, under unfavourable conditions, they produce spores. These qualifications matter: one feature or activity should not be applied to every bacterium.

How are bacteria useful or harmful in daily life?

Bacterial activities affect food, soil and health. The majority of heterotrophic bacteria are important decomposers, organisms that break down dead organic material. Organic material here means material originating from living things. Decomposition helps return substances from dead remains to the surroundings.

Which bacterial activities are useful?

• Curd formation: bacteria help change milk into curd, providing a familiar example of a useful microbial activity.
• Antibiotic production: some bacteria are used to produce antibiotics, substances that kill or inhibit the growth of certain disease-causing microbes.
• Nitrogen fixation: some bacteria convert atmospheric nitrogen into forms plants can use. Nitrogen is a nutrient needed for making substances such as proteins.
• Decomposition: many bacteria break down dead material and contribute to the recycling of nutrients, substances organisms need for growth and maintenance.

Which effects are harmful?

A pathogen is a disease-causing organism or agent. Some bacteria are pathogens affecting people, crops and other animals. Cholera, typhoid and tetanus are examples of bacterial diseases in humans. Citrus canker is a bacterial disease of citrus plants.

Bacterial growth can also contribute to food going bad. This helps explain why the presence of microbes matters when food is stored. However, useful curd formation and harmful food spoilage must not be treated as identical outcomes merely because bacteria are involved.

When describing a useful or harmful effect, connect the activity with its result. “Making curd from milk” states a clear use. “Causing citrus canker” states a specific harmful effect. Saying that all bacteria cause disease ignores their useful roles in daily life and nature.

How is Amoeba organised, and how does it obtain food?

Amoeba is a microscopic, single-celled organism found in pond water. It belongs to Protista and has a membrane-bound nucleus. Members of Protista are primarily aquatic, meaning associated with water. Their nutrition varies, so Amoeba does not represent every protist's way of obtaining food.

What structures does Amoeba have?

Amoeba has a cell membrane, a rounded nucleus and cytoplasm, the jelly-like material within the cell around the nucleus. Its cytoplasm contains vacuoles, small enclosed spaces. A food vacuole is a space in which engulfed food is held and digested.

Amoeba constantly changes its shape and position. It extends pseudopodia, temporary finger-like projections also called false feet. The singular is pseudopodium. These projections help in locomotion, movement from place to place, as well as in capturing food.

The drawing shows an irregular cell with projecting parts. Its labels identify the nucleus, a pseudopodium, a food particle being ingested, food vacuoles and egested waste. The food particle is shown near a projection at the cell edge.

See Fig. 2.10 in your NCERT textbook

What happens to a food particle?

1. Ingestion, or taking in food: pseudopodia extend around a food particle and engulf it. The food becomes enclosed in a food vacuole.
2. Digestion, or breaking food into simpler substances: digestive juices act on the food inside the vacuole.
3. Absorption, or taking digested substances into the cell's cytoplasm: the simpler substances pass out of the food vacuole into the surrounding cytoplasm.
4. Assimilation, or using absorbed food: the substances support growth, maintenance and multiplication of the organism.
5. Egestion, or removing undigested food: the undigested residue is expelled outside the cell.

This is holozoic nutrition, in which food is taken in and then digested within the body. Amoeba carries out these functions within one cell. It has no separate mouth, stomach or intestine like the specialised digestive organs of many multicellular animals.

The link between structure and function is important. Pseudopodia are associated with food capture and movement; food vacuoles are associated with digestion. A food vacuole is not a permanent stomach, and a pseudopodium is not a fixed leg.

How does Amoeba respire and remove wastes?

Respiration is the cellular process that releases usable energy from food. Amoeba needs this energy for its life activities. It exchanges gases across its cell membrane rather than through specialised organs such as lungs.

How do gases cross the cell surface?

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Concentration means the amount of a substance in a given space. Oxygen dissolved in the surrounding water diffuses into Amoeba.

The oxygen is used in respiration. Carbon dioxide produced during respiration diffuses out into the surrounding water. Taking in oxygen and removing carbon dioxide are gas exchange; releasing energy from food is the purpose of cellular respiration.

What is the difference between excretion and egestion?

Excretion is the removal of waste substances produced by the cell's chemical activities. Dissolved metabolic wastes, meaning wastes of those activities, can diffuse out across Amoeba's cell membrane. Egestion removes undigested food that has not been absorbed and used.

The contractile vacuole collects and expels excess water. It helps maintain water balance, meaning a suitable amount of water inside the cell. It should not be confused with a food vacuole, which is involved in digestion.

Note: An undigested food particle leaving Amoeba is an example of egestion. Carbon dioxide leaving after respiration is an example of waste removal. These materials have different origins, even though both leave the same single cell.

Amoeba's cell surface is directly exposed to its watery surroundings. This allows exchange across that surface. The same explanation cannot simply be applied to every cell deep inside a large multicellular organism, where many cells are not in direct contact with the external environment.

How does Amoeba reproduce by binary and multiple fission?

Asexual reproduction produces new individuals from a single parent without the fusion of reproductive cells. Amoeba reproduces asexually by fission. The original organism is the parent, and the new organisms produced are called daughter individuals.

What happens during binary fission?

Binary fission is division of one parent into two daughter individuals. In Amoeba, division can take place in any plane, meaning that there is no fixed direction in which the body must split.

1. The parent Amoeba is a single cell containing its nucleus and cytoplasm before division begins.
2. The nucleus divides, producing two daughter nuclei within the parent cell.
3. The cytoplasm divides so that each developing daughter cell receives a nucleus.
4. Two separate daughter Amoebae are formed, each capable of carrying out its own life processes.

The sequence of drawings follows one irregular Amoeba as it changes shape and divides. Arrows connect the successive stages, ending with two separate daughter cells.

See Fig. 7.1(a) in your NCERT textbook

How is multiple fission different?

Multiple fission produces many daughter individuals from one parent. Under unfavourable conditions, Amoeba can form a protective covering called a cyst. Inside it, repeated nuclear divisions are followed by division of the cytoplasm around the nuclei, forming many small Amoebae.

When conditions become favourable, the cyst wall breaks and the daughter Amoebae are released. A cyst is a protective stage, not the name of a new kingdom. Multiple fission differs from binary fission in the number of daughter individuals produced from one parent.

Keep the sequence clear: nuclear division must be linked with the formation of daughter cells. Merely saying that the organism develops several nuclei does not complete an explanation of reproduction, because new individuals must also be formed.

How is bread mould structured, nourished and supplied with energy?

Fungi are eukaryotic heterotrophs. Mould is a fungus with a thread-like body; Rhizopus is a bread mould. With the exception of unicellular yeasts, fungi are filamentous, meaning composed of thread-like structures.

The individual threads are called hyphae, with hypha as the singular. Their network forms the mycelium. Fungal cell walls contain chitin. The spreading threads are not the same structures as the rounded spore-containing bodies involved in reproduction.

How does mould obtain food?

Most fungi absorb soluble organic matter from dead material. This is saprotrophic nutrition, also called saprophytic nutrition. Bread mould releases digestive substances onto its food, breaks complex food down outside its body and absorbs the simpler soluble products.

The place where digestion occurs distinguishes mould from Amoeba. Mould digests food outside its body before absorption. Amoeba engulfs food and digests it inside a food vacuole. Both are heterotrophs, but the steps by which food enters their cells differ.

How does mould respire?

Bread mould carries out aerobic respiration, respiration using oxygen. Oxygen reaches its cells by diffusion. The absorbed food is broken down to release energy, with carbon dioxide and water produced. The mould needs this energy for growth and other life activities.

How can spores form new mould?

A sporangium is a spore-containing structure; the plural is sporangia. In Rhizopus, these structures appear as small rounded bodies on stalks. The spores have protective walls and can develop into new individuals on a suitable moist surface.

1. Spores develop within the sporangia, the rounded reproductive structures of the bread mould.
2. The spores are released from these structures and can reach other surfaces.
3. Their protective walls help them persist until they encounter suitable conditions for growth.
4. On a suitable moist surface, a spore begins to grow and develops into a new Rhizopus individual.

The drawing shows a cluster of upright stalks ending in rounded structures, with branching threads below. Small particles near an opened structure are labelled Spores.

See Fig. 7.6 in your NCERT textbook

Which fungi are useful, and which effects are harmful?

Fungi occur in air, water, soil and on plants and animals. They prefer warm and humid places; humid means containing much moisture in the air. Their effects depend on the fungus and on where and how it grows.

What useful roles do fungi perform?

Yeast is a unicellular fungus used in making bread and beer. Edible mushrooms provide another familiar use of fungi. Some fungi are sources of antibiotics; Penicillium is an example. Many fungi also decompose dead material, helping substances return to the environment.

These examples show why fungi should not be described simply as pests. The same kingdom contains organisms associated with food production, medicines and decomposition. The fact that yeast has one cell does not remove it from the fungal kingdom.

What harmful effects do fungi have?

Fungi may grow on moist bread and rotten fruits, contributing to spoilage. Some cause diseases in plants and animals. Puccinia is a fungus that causes wheat rust, a plant disease. White patches on mustard leaves can also be caused by a parasitic fungus.

A parasite obtains nourishment from a living organism called its host, at the host's expense. Parasitic fungi therefore differ from saprotrophic fungi in their source of food. One depends on living hosts, whereas the other absorbs nutrients from dead material.

Some fungi also live in mutually useful associations with other organisms. Thus, “heterotrophic” does not mean “disease-causing”. It describes dependence on an external source of organic food. Use a named example when explaining either a useful activity or a harmful effect.

What are the main characteristics of kingdom Plantae?

Plantae includes the organisms commonly called plants. Their cells are eukaryotic and have cell walls mainly made of cellulose. Green plant cells contain chloroplasts, structures containing chlorophyll, the green pigment that captures light energy.

How do green plants make food?

Photosynthesis is the preparation of food from carbon dioxide and water using light energy captured by chlorophyll. Green plants use this process to make carbohydrates, food substances that include sugars and starch. Oxygen is released during the process.

Photosynthetic nutrition is autotrophic. It differs from the absorption of food by fungi and the ingestion of food by animals. The shared presence of a cell wall in fungi and plants does not remove this important difference in nutrition.

Are all plants completely independent for food?

A few members are partially heterotrophic. Insectivorous plants, meaning insect-eating plants, include the Venus flytrap and bladderwort. Cuscuta is a parasitic plant that obtains ready-made food from its host. It does not have chlorophyll.

These examples show why a classification description must leave room for stated exceptions. Do not replace a description of green plants with the claim that every plant makes all its own food. Cell structure and other features must be considered alongside nutrition.

Sketch a plant showing roots, a stem, leaves and a flower. Label each part. Beside a leaf, write that chlorophyll captures light energy for photosynthesis. Keep this as a general plant sketch rather than a classification chart of plant groups.

What distinguishes Animalia and vertebrates?

Animalia consists of multicellular, eukaryotic heterotrophs whose cells lack cell walls. Animals depend directly or indirectly on plants for food. Their nutrition involves taking in food and digesting it within the body. Most animals are capable of locomotion.

How are animal bodies organised?

Animal organisation varies. In sponges, cells form loose groups. In more complex animals, cells form tissues and organs. An organ system is a group of organs working together to perform a major function, such as digestion.

Increasing organisation allows different parts to specialise in different functions. Classification reflects these differences as well as relationships among groups. Complex forms of life have evolved from simpler forms; this does not mean that every present-day simple organism must turn into a complex animal.

What makes an animal a vertebrate?

Vertebrates are animals with a vertebral column, or backbone. This supporting structure is made of bone or cartilage, a firm, flexible supporting tissue. Animals without a backbone are called invertebrates.

The familiar vertebrate groups include fishes, amphibians, reptiles, birds and mammals. Amphibians, such as frogs, can live in water as well as on land. Birds have feathers. Mammals have milk-producing glands. These are group features, rather than definitions of all animals.

The absence of a backbone does not mean the absence of support. Arthropods, for example, have an outer supporting covering. A shell or an outer skeleton is not a vertebral column, so the position and nature of the supporting structure matter.

Sketch an elongated body with repeated ring-like segments. Label the segments and identify it as an earthworm, an annelid invertebrate. The drawing should show an animal example without suggesting that all animals have the same body form.

How can the main invertebrate groups be distinguished?

A phylum, plural phyla, is a major group within a kingdom. Animal phyla can be distinguished by features of their body plan. Learn each group through its distinguishing characteristics and examples, rather than through its name alone.

What do the comparison terms mean?

Bilateral symmetry means that one plane can divide the body into matching left and right halves. Radial symmetry means that planes through a central axis divide the body into similar halves. Sponges are mostly asymmetrical, meaning they do not have such a regular division into matching halves.

A segment is one of a series of repeated body divisions. An appendage is a projecting body part. An exoskeleton is an outer supporting covering. These terms help distinguish animals that may otherwise appear superficially similar.

A cross-section is a slice across the body. The digestive tract is the passage through which food travels; its anus is the opening for undigested waste. A water vascular system is a system of water-filled canals characteristic of echinoderms.

Which distinctions need particular care?

Cnidaria and Coelenterata are names used here for the same group, so Hydra and Aurelia must not be learnt as belonging to two separate groups merely because both names occur. Nematoda refers to roundworms, represented by Ascaris and Wuchereria.

Flatworms and roundworms differ in body form. Earthworms are annelids with repeated segments. Arthropods have jointed appendages as well as an outer skeleton. A general worm-like appearance is therefore insufficient to identify a phylum.

Adult echinoderms have radial symmetry, but their larvae, the early stages before adulthood, have bilateral symmetry. Retain the word “adult” when stating the radial symmetry of a starfish. Also retain “mostly” when describing sponges as asymmetrical.

For each group, pair the two features with the two examples. The features explain why the examples belong together. A complete comparison names the group, states observable or structural distinctions, and uses examples that fit those distinctions.

Glossary

• Classification — The arrangement of living organisms into groups according to their shared characteristics.
• Kingdom — A broad classification group containing organisms that share important basic characteristics.
• Prokaryotic — Describing a cell whose genetic material is not enclosed within a membrane-bound nucleus.
• Eukaryotic — Describing a cell with a nucleus surrounded by a nuclear membrane.
• Autotrophic nutrition — A mode of nutrition in which organisms make food from simple substances.
• Heterotrophic nutrition — A mode of nutrition involving dependence on other organisms or their products for food.
• Pseudopodia — Temporary projections of Amoeba's cell used for movement and the capture of food.
• Food vacuole — An enclosed space in Amoeba in which engulfed food is held and digested.
• Diffusion — The net movement of particles from higher concentration towards a region of lower concentration.
• Excretion — The removal of waste substances produced by the chemical activities of living cells.
• Binary fission — A form of asexual reproduction in which one parent divides into two daughter individuals.
• Multiple fission — A form of asexual reproduction producing many daughter individuals from a single parent organism.
• Mycelium — The network of fine threads called hyphae that forms the body of a filamentous fungus.
• Saprotrophic nutrition — Obtaining nourishment by digesting dead organic material externally and absorbing the soluble products.
• Vertebrate — An animal with a vertebral column, or backbone, made of bone or cartilage.

Common errors and misconceptions

• Misconception: Every organism with a cell wall is a plant. Correct: Fungi and bacteria also have cell walls. Cell structure and nutrition must be considered together when assigning a kingdom.
• Misconception: All bacteria are harmful. Correct: Many are useful in decomposition, curd formation, antibiotic production or nitrogen fixation. Some bacteria cause diseases.
• Misconception: Amoeba belongs to Monera because it has one cell. Correct: Amoeba has a membrane-bound nucleus and belongs to Protista; Monera contains prokaryotic organisms.
• Misconception: Egestion and excretion mean the same thing. Correct: Egestion removes undigested food, whereas excretion removes wastes produced by the cell's chemical activities.
• Misconception: Fungi swallow food like Amoeba. Correct: Bread mould digests food outside its body and absorbs the soluble products. Amoeba digests engulfed food inside food vacuoles.
• Misconception: Every plant makes all its own food. Correct: Cuscuta is parasitic, and a few plants are partially heterotrophic. Green plants carry out photosynthesis.
• Misconception: Cnidaria and Coelenterata are separate groups in this comparison. Correct: The names refer here to the same group, represented by Hydra and Aurelia.
• Misconception: All stages of an echinoderm have radial symmetry. Correct: Adults have radial symmetry, but larvae have bilateral symmetry. The stage of life must be specified.

Exam-style questions with model answers

Q1. Monera contains prokaryotic organisms, while Protista includes unicellular eukaryotes. A bacterium lacks a membrane-bound nucleus, whereas single-celled Amoeba has one. Assign each organism to its kingdom and give the stated reason. [2 marks]

1. The bacterium belongs to Monera because its cell lacks a membrane-bound nucleus.
2. Amoeba belongs to Protista because it is a single-celled organism with a membrane-bound nucleus.

Q2. Bacterial shape names are cocci for spheres, bacilli for rods, vibrio for commas and spirilla for spirals. Identify the group for a spherical bacterium and a comma-shaped bacterium. [2 marks]

1. The spherical bacterium belongs to the cocci shape group because its cell has a rounded form.
2. The comma-shaped bacterium belongs to the vibrio shape group because its cell has the stated curved form.

Q3. Bacteria help make curd from milk and convert atmospheric nitrogen into forms plants can use. Some other bacteria cause cholera in humans or citrus canker in citrus plants. Explain two useful effects and two harmful effects using these facts. [4 marks]

1. Curd formation is a useful effect because bacterial activity helps turn milk into curd, a food used in daily life.
2. Nitrogen fixation is useful because bacteria convert atmospheric nitrogen into forms that plants can absorb and use.
3. Some bacteria cause cholera, illustrating a harmful effect of bacterial activity on human health.
4. Other bacteria cause citrus canker, illustrating that harmful bacteria can affect crop plants as well as humans.

Q4. In Amoeba, pseudopodia surround food, a food vacuole encloses it, digestive juices simplify it, digested substances enter the cytoplasm and support growth and maintenance, and the undigested residue leaves the cell. Explain the five stages: ingestion, digestion, absorption, assimilation and egestion. [5 marks]

1. Ingestion is the taking in of food. Amoeba extends pseudopodia around the food particle and encloses it within a food vacuole.
2. Digestion occurs inside the food vacuole. Digestive juices act on the enclosed food and break it down into simpler substances.
3. Absorption follows digestion. The simpler, digested substances pass from the food vacuole into the cytoplasm of the same cell.
4. Assimilation is the use of the absorbed substances. Amoeba uses them for activities including growth and maintenance of its body.
5. Egestion is the removal of the undigested residue. The material that remains after digestion is expelled outside the cell.

Q5. Amoeba takes in dissolved oxygen and releases carbon dioxide across its cell membrane by diffusion. Its chemical activities also produce dissolved wastes, while undigested food remains in food vacuoles. Explain gas exchange, excretion and egestion using these facts. [3 marks]

1. Gas exchange occurs by diffusion across the cell membrane: dissolved oxygen enters Amoeba and carbon dioxide moves out into the surrounding water.
2. Excretion removes wastes produced by the cell's chemical activities. The dissolved metabolic wastes are different from food that has simply remained undigested.
3. Egestion removes the undigested food residue from food vacuoles to the outside. It is therefore distinguished from excretion by the origin of the material removed.

Q6. In binary fission, one Amoeba's nucleus divides into two, its cytoplasm divides, and two daughter cells form. In multiple fission, a protective cyst surrounds the parent, repeated nuclear divisions and division of cytoplasm produce many daughters, and they are released when favourable conditions return. State four differences using these facts. [4 marks]

1. Binary fission produces two daughter Amoebae from one parent, whereas multiple fission produces many daughter Amoebae from the same parent.
2. In binary fission the nucleus divides into two; in multiple fission repeated nuclear divisions produce several nuclei before daughter formation is completed.
3. The described multiple-fission process occurs within a protective cyst, whereas the described binary-fission process directly divides the parent cell.
4. Binary fission ends with two separate daughter cells; in the described multiple-fission process, daughters are released from the cyst when favourable conditions return.

Q7. Rhizopus has threads called hyphae forming a mycelium, digests food outside its body and absorbs soluble products, uses oxygen to release energy from food, and forms spores inside sporangia. Describe its body, nutrition, respiration and reproduction in five points, separating external digestion from absorption. [5 marks]

1. The body of Rhizopus consists of fine threads called hyphae. The network formed by these threads is known as the mycelium.
2. Its digestion takes place outside the body. Food is broken down externally into simpler substances before those substances enter the fungal cells.
3. The soluble products of digestion are absorbed into the fungus. External digestion and absorption are therefore successive parts of its nutrition.
4. Rhizopus uses oxygen in respiration to release energy from food. This process provides the energy required for its living activities.
5. Its sporangia contain spores, which are involved in reproduction. These reproductive structures must be distinguished from the network of hyphae forming its body.

Q8. Use this key: Porifera have pores and loose cell groups; Cnidaria have radial symmetry and stinging cells; Annelida have repeated segments and bilateral symmetry; Arthropoda have jointed appendages and a chitinous exoskeleton; Echinodermata are marine and have a water vascular system. Match each description to its group and repeat both identifying features. [5 marks]

1. Porifera is the group identified by pores in the body and organisation as loose groups of cells. Both features together support this identification.
2. Cnidaria is identified by radial symmetry and specialised stinging cells. The body arrangement and the presence of these cells provide the stated clues.
3. Annelida is identified by repeated body segments and bilateral symmetry. The two supplied features describe the body's divisions and its arrangement into halves.
4. Arthropoda is identified by jointed appendages and a chitinous exoskeleton. The outer covering and jointed projecting parts form the distinguishing combination.
5. Echinodermata is identified by its marine habitat and water vascular system. The key combines where these animals live with a characteristic internal system.

Key takeaways

• Classification groups organisms by shared characteristics and makes their similarities, differences and relationships easier to study systematically.
• The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia; cell structure and nutrition help distinguish them.
• Bacteria have several shapes and include useful decomposers and food-producing forms as well as disease-causing forms.
• Amoeba uses pseudopodia for movement and food capture, then digests its food inside a food vacuole.
• Binary fission produces two daughter individuals, whereas multiple fission produces many daughter individuals from one parent.
• Bread mould has a network of hyphae, digests food externally, absorbs soluble products and can reproduce through spores.
• Green plants use chlorophyll to capture light for photosynthesis, but some plants depend partly or wholly on other organisms for nutrients.
• Vertebrates have backbones; invertebrate phyla are distinguished by body features such as pores, segments and jointed appendages.

Test yourself

Why does the presence of a cell wall not prove that an organism is a plant?

Fungi and bacteria also have cell walls. Cell structure, organisation and mode of nutrition must be considered together.

Which kingdom contains Amoeba, and what cell feature helps identify it?

Amoeba belongs to Protista. It is a single-celled organism with a membrane-bound nucleus.

What two functions do pseudopodia perform in Amoeba?

Pseudopodia help Amoeba move from place to place and surround food particles for ingestion.

How do a food vacuole and a contractile vacuole differ?

A food vacuole contains food being digested. A contractile vacuole collects and expels excess water.

What distinguishes binary fission from multiple fission?

Binary fission produces two daughter individuals from one parent; multiple fission produces many daughter individuals.

What is the relationship between a hypha and a mycelium?

A hypha is one fungal thread. A network of such threads forms the mycelium.

Why must Cnidaria and Coelenterata be linked in this classification?

They are names used for the same group here, including Hydra and Aurelia as examples.

Which qualification is needed when describing echinoderm symmetry?

Adult echinoderms have radial symmetry, whereas their larvae have bilateral symmetry.