CLASSIFICATION

Question 1

morphology anatomy

Answer 1

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). Vertebrates all have a vertebral column, 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.

Question 2

sequence of dna

Answer 2

The sequences of DNA and of amino acids in proteins are used as a more accurate means of classification than studying morphology and anatomy. Eukaryotic organisms contain chromosomes, made up of strings of genes. Genes are made of DNA, which is composed of a sequence of bases (see Chapter 4). 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. The process of biological classification called cladistics involves organisms being grouped together according to whether or not they have one or more unique characteristics in common derived from the group’s last common ancestor, which are not present in more distant ancestors. Organisms that share a more recent ancestor (and are more closely related) have DNA base sequences that are more similar than those that share only a distant ancestor.

Question 3

Characteristics of living organisms

Answer 3

There are seven characteristics that all living things show, including plants and other organisms. These characteristics are movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. You need to be able to recall and describe these. You may be given a picture of a living thing to study and then asked to identify which characteristics you can observe by watching it for a few minutes. Some of the seven would not be suitable answers, e.g. growth, respiration, reproduction (these are not likely to be visible or observable in a short time span). Some non-living things, such as cars, may appear to show some of the characteristics, but not all of them.

Question 4

Species

Answer 4

A group of organisms that can reproduce to produce fertile offspring

Question 5

Binomial system

Answer 5

An internationally agreed system in which the scientific name of an organism is made up of two parts: the genus and the species

Question 6

Nutrition

Answer 6

The taking in of materials for energy, growth and development. Plants require light, carbon dioxide, water and ions. Animals need organic compounds and ions and usually need water

Question 7

Excretion

Answer 7

The removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials and substances that are in excess of requirements

Question 8

Respiration

Answer 8

The chemical reactions in cells that break down nutrient molecules and release energy for metabolism .

Question 9

Sensitivity

Answer 9

The ability to detect or sense stimuli in the internal or external environment and to respond appropriately

Question 10

Growth

Answer 10

A permanent increase in size and dry mass by an increase in cell number or cell size, or both

Question 11

Movement

Answer 11

An action by an organism or part of an organism causing a change of position or place

Question 12

The cells of all living organisms contain

Answer 12

cytoplasm, a cell membrane and DNA as genetic material.

Question 13

plants

Answer 13

Plants are made up of many cells – they are multi-cellular. Plant cells have an outside wall made of cellulose. Many of the cells in plant leaves and stems contain chloroplasts with photosynthetic pigments, e.g. chlorophyll. Plants make their food through photosynthesis.

Question 14

Animals

Answer 14

Animals are multi-cellular organisms whose cells have no cell walls or chloroplasts. Most animals ingest solid food and digest it internally. For the Core syllabus, you only need to learn the main groups of vertebrates and arthropods.

Question 15

Classification of vertebrates

Answer 15

Vertebrates are animals with backbones (part of an internal skeleton). Vertebrates are divided into five groups called classes. Details of each group are given in the table below. You only need to be able to describe visible external features, but other details can be helpful (see the ‘Other details’ column).

Question 16

Classification of arthropods

Answer 16

Special features of arthropods:

• they are invertebrates – they have no backbone; • they have an exoskeleton that is waterproof – making arthropods an extremely successful group, as they can exist in very dry places – and they are not confined to water or moist places like most invertebrates;
• their bodies are segmented;
• they have jointed limbs (the exoskeleton would prevent movement). There are more arthropods than any other group of animals, so they are divided into classes. Figure 1.2 shows the differences between the four classes – insects, arachnids, crustaceans and myriapods. You only need to know about their external features.

Answer 17

In addition to the main features of all living organisms, you need to be aware that cells of living organisms also contain ribosomes in the cytoplasm, floating freely or attached to membranes called rough endoplasmic reticulum. Ribosomes are responsible for protein synthesis. Enzymes are involved in respiration. In the classification of living organisms, there are five kingdoms, each with its own special and obvious features. The kingdoms are as follows:

• Animals – multi-cellular organisms that have to obtain their food. Their cells do not have walls.
• Plants – multi-cellular organisms with the ability to make their own food through photosynthesis because of the presence of chlorophyll. Their cells have walls (containing cellulose).
• Fungi – many are made of hyphae, with nuclei and cell walls (containing chitin) but no chloroplasts.
• Prokaryotes (bacteria) – very small and single celled, with cell walls but no nucleus. • Protoctists – single celled with a nucleus. Some have chloroplasts.

Question 18

Features of the plant kingdom

Answer 18

You only need to learn the features of flowering plants and ferns. Flowering plants are all multi-cellular organisms. Their cells have cellulose cell walls and sap vacuoles. Some of the cells contain chloroplasts. They have roots, stems and leaves. Reproduction can be by producing seeds, although asexual reproduction is also possible. There are two groups – monocotyledons and dicotyledons. The term cotyledon means ‘seed leaf’. The main differences between the two groups are shown in the table below.

Question 20

ferns

Answer 20

Ferns are land plants. Their stems, leaves and roots are very similar to those of the flowering plants. The stem is usually entirely below ground and takes the form of a structure called a rhizome. The stem and leaves have sieve tubes and water-conducting cells. Ferns also have multi-cellular roots with vascular tissue. The leaves are several cells thick. Most of these have an upper and lower epidermis, a layer of palisade cells and a spongy mesophyll. Ferns do not form buds. The midrib and leaflets of the young leaf are tightly coiled and unwind as it grows. Ferns produce gametes but no seeds. The zygote gives rise to the fern plant, which then produces single-celled spores from numerous sporangia (spore capsules) on its leaves. The sporangia are formed on the lower side of the leaf.

Question 21

features of virus

Answer 21

Question 22

Tissue .

Answer 22

A group of cells with similar structures working together to perform a shared function (job)

Question 23

Organ

Answer 23

A structure made up of a group of tissues working together to perform specific functions

Question 24

Organ system

Answer 24

A group of organs with related functions working together to perform body functions

Question 25

Cell structure and organisation

Answer 25

Most living things are made of cells – microscopic units that act as building blocks. Multi-cellular organisms are made up of many cells. Cell shape varies depending on its function (what job it does). Plant and animal cells differ in size, shape and structure (see Figure 2.1). Plant cells are usually larger than animal cells.

Question 26

parts of a cell

Answer 26

Question 27

other structures in the cytoplasm:

Answer 27

ribosomes (found on rough endoplasmic reticulum), mitochondria and vesicles. Only prokaryotes (bacteria) do not have these features.

Ribosomes are responsible for the synthesis of proteins from amino acids (see Chapter 17).

Mitochondria (singular: mitochondrion) are where aerobic respiration takes place. Cells with high rates of metabolism, e.g. liver cells, shown in Figure 2.3, require large numbers of mitochondria to provide sufficient energy.

Vesicles are bubbles of liquid surrounded by a membrane. They transfer chemicals such as enzymes around the cell, or release their contents out of the cell.

Question 29

animal cells

Answer 29

Question 30

plant cells

Answer 30

Question 31

size of specimen

Answer 31