Solving a biological problem: Class 9 Biology

Key points

Biology is the scientific study of living things. The word comes from the Greek bios (life) and logos (study). It deals with the structure, function, growth, origin, evolution and distribution of organisms. Knowledge of biology helps us to improve health, food production and the care of the environment.

Some main branches of biology:

• Morphology: study of the form and external structure of organisms.
• Anatomy: study of the internal structure of organisms.
• Physiology: study of the functions of the body and its parts.
• Cell biology (cytology): study of the structure and working of cells.
• Genetics: study of heredity and variation.
• Ecology: study of the relationship of organisms with each other and with their environment.
• Taxonomy: classification and naming of organisms.
• Microbiology: study of microscopic organisms such as bacteria, viruses and some fungi.
• Biotechnology: use of living organisms or their parts to make useful products.
• Embryology, palaeontology, parasitology and immunology deal with development, fossils, parasites and defence against disease.

Levels of biological organisation, from smallest to largest:

• Molecules: atoms join to form molecules such as water, proteins and DNA.
• Organelles: parts of a cell, such as the nucleus and mitochondria.
• Cells: the basic unit of life.
• Tissues: groups of similar cells doing one job.
• Organs: tissues combined to do a special task, such as the heart.
• Organ systems: organs working together, such as the digestive system.
• Organism: the complete living individual.
• Population, community, ecosystem, biome and biosphere: groups of organisms and their surroundings, up to the whole living part of the Earth.

A biological problem is a question about living things that can be answered by observation and experiment. Biologists solve such problems by the biological method, which is the scientific method applied to living systems. It is a logical, step by step way of finding reliable answers.

Steps of the biological method:

• Recognising a problem: noticing something that needs an explanation, for example plants near a window bend towards the light.
• Observation: collecting information with the senses or instruments, in a careful and unbiased way.
• Hypothesis: a tentative, testable explanation, for example 'plants bend towards light because light affects the growth of the shoot'.
• Deductions: predictions about what should happen if the hypothesis is true, often written as an 'if... then' statement.
• Experimentation: a planned test carried out under controlled conditions.
• Results and conclusion: the data are recorded and analysed, and the hypothesis is accepted, changed or rejected.
• Reporting: the work is written up so that others can repeat and check it.

A good hypothesis must be testable and must be possible to prove wrong. A hypothesis that is supported by many experiments over a long time may become a theory, which is a well tested explanation of a wide range of observations. A law (or principle) describes a regular pattern that is always found in nature, such as Mendel's law of segregation.

In an experiment, a variable is any factor that can change. The independent variable is the one the investigator deliberately changes. The dependent variable is the one that is measured as a result. All other factors that could affect the result are controlled variables and must be kept the same. A control experiment is a setup identical to the test setup except that the factor under test is missing. It shows that the result is due to that factor alone.

Experiments should be repeated several times and use many samples, so that chance effects are reduced. Data are recorded in tables and shown as graphs, bar charts or pie charts. A line graph suits two continuous variables, a bar chart suits separate categories, and a pie chart shows parts of a whole. Averages (the mean) are calculated, and the conclusion must follow from the data and not from what the investigator hoped to find.

Inductive reasoning moves from many specific observations to a general rule. Deductive reasoning moves from a general idea to a specific prediction. Both are used in science. Biologists also use instruments such as the light microscope, the electron microscope, centrifuges and computers to collect and study data.

Muslim scientists made important contributions to the biological method and to biology. Ibn al-Haitham stressed observation and experiment for testing ideas. Al-Jahiz wrote the Book of Animals, discussing food chains and the effect of the environment on animals. Ibn Sina wrote the Canon of Medicine, used in Europe for centuries. Al-Zahrawi described many surgical instruments and methods. Ibn al-Nafis described the flow of blood through the lungs. Al-Dinawari wrote on plants.

Biology offers many careers: doctor, surgeon, dentist, nurse, pharmacist, nutritionist, agriculturist, forester, biotechnologist, microbiologist, teacher and environmental scientist. A student who understands the biological method can plan investigations, judge claims fairly and make sound decisions on matters of health and environment.

Study tip: Learn the order of the biological method and the order of the levels of organisation by heart, since both are asked often. In any experiment question, always name the independent variable, the dependent variable, the controlled variables and the control. Practise drawing a neat table and a labelled graph with units on both axes.

Definitions and flashcards

Say the meaning first, then open the card to check.

Short questions with model answers

These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.

Common mistakes

• Mixing up a hypothesis and a theory. A hypothesis is a testable guess, while a theory is strongly supported by evidence.
• Changing more than one factor in an experiment, so that the cause of the result cannot be known.
• Writing the independent and dependent variables the wrong way round. The independent one is changed, the dependent one is measured.
• Forgetting to give a control, or using a control that differs from the test in more than one way.
• Placing organisation levels in the wrong order, for example putting tissue above organ.

Practise this chapter

Practice questions and timed test Printable worksheet