Unit B2 - The Components of Life

Content and How Science Works overview

The three topics in Unit B2 allow a more in-depth study of the structure, development and functioning of organisms. This includes the role of various organ systems in animals and plants.

Practical work throughout the unit will give students opportunities to plan and carry out investigations. They will devise their own models and evaluate them, assess and manage risks, trial their plans and consider how the quality of their data might be improved. They will analyse data, draw conclusions providing evidence to support their conclusions, and evaluate to what degree the conclusions support the hypothesis.

Throughout the unit, students will have the opportunity to improve and demonstrate mathematical skills, including understanding number size and scale, using estimation, understanding and using direct proportion and simple ratios, calculating arithmetic means, plotting and drawing graphs (line graphs, bar charts, pie charts, scatter graphs, histograms) selecting appropriate scales for the axes, translating information between graphical and numeric form, extracting and interpreting information from charts, graphs and tables and understanding the idea of probability.

Topic 1 compares the structure of animal, bacterial and plant cells. Students will learn about the relationship between genes and DNA and find out how cells divide. Exciting scientific developments such as genetic engineering, the Human Genome Project and the use of stem cells are key aspects of this topic. Enzyme properties and the principles of enzyme action are important areas of biology also covered.

The impact of developments in science, including the advantages, disadvantages and risks, will be covered in relation to genetic modification and cloning. There will be opportunities to explore the issues raised by social, economic and environmental effects of developing scientific knowledge, such as in cloning and stem cell research.

Work on cell structure, protein synthesis and the way enzymes work will give students experience in evaluating models and their importance in the development of our understanding of biological processes. Students will also explore the way that scientific ideas develop as a result of the collaboration of scientists, such as in the Human Genome Project, and the importance of creative thought in developing ideas, such as how DNA structure links to protein structure.

In Topic 2 students will learn about the differences between aerobic and anaerobic respiration and investigate the relationship between exercise, breathing rate and heart rate. They go on to study important processes in plants including photosynthesis and water movement. The final section of Topic 2 allows students to explore the relationship between organisms and their environment.

Unit B2: The components of life

Students will be expected to present data that they have collected, using the appropriate conventions and language, in order to develop arguments and draw conclusions when investigating photosynthesis and respiration. Students will also evaluate ‘scientific’ claims made in the media about new scientific developments, such as in adverts for energy-boosting products, and how science as yet does not have answers to some questions about these.

Topic 3 includes an interesting study of fossils and the fossil record. Students will also learn about the structure and functions of blood and the heart, and look at the role of blood vessels. Parts of the digestive system and their functions are key areas of human biology and up-todate issues such as the use of prebiotics and probiotics are discussed.

Students will also evaluate ‘scientific’ claims made in the media about new scientific developments, such as in adverts for probiotics, and how science as yet does not have answers to some questions about these.

Assessment overview

This unit is externally assessed, through a one hour, 60 mark, tiered written examination, containing six questions.

The examination will contain a mixture of question styles, including objective questions, short answer questions and extended writing questions.

Unit B2: The components of life

Practical investigations in this unit Within this unit, students will develop an understanding of the process of scientific investigations, including that investigations:

• use hypotheses which are tested

• require assessment and management of risks

• require the collection, presentation, analysis and interpretation of primary and secondary evidence including the use of appropriate technology

• should include a review of methodology to assess fitness for purpose

• should include a review of hypotheses in the light of outcomes.

The following specification points are practical investigations which that exemplify the scientific process and may appear in the written examination for this unit:

1.8 Investigate how to extract DNA from cells

1.32 Investigate the factors that affect enzyme activity

2.5 Investigate the effect of exercise on breathing rate and heart rate

2.16 Investigate how factors, including the effect of light intensity, CO2 concentration or temperature, affect the rate of photosynthesis

2.21 Investigate osmosis

2.22 Investigate the relationship between organisms and their environment using fieldwork techniques

2.23 Investigate the distribution of organisms in an ecosystem, using sampling techniques including:

- pooters

- sweep nets/pond nets

- pitfall traps

- quadrats

and measure environmental factors including:

- temperature

- light intensity

- pH

3.17 Investigate the effect of different concentrations of digestive enzymes, using and evaluating models of the alimentary canal

The following are further suggestions for practical work within this unit:

• Investigate plant and animal cells with a light microscope

• Investigate the effect of concentration on rate of diffusion

• Investigate the effect of glucose concentration on rate of anaerobic respiration in yeast

• Investigate the increase in heart rate and/or breathing rate with exercise

Unit B2: The components of life

• Investigate how the structure of the leaf is adapted for photosynthesis

• Investigate how the loss of water vapour from leaves drives transpiration

The controlled assessment task (CAT) for the GCSE in Biology will be taken from any of these practical investigations (specification points and further suggested practical work). This task will change every year, so future CATs will be chosen from this list.

Unit B2: The components of life

Detailed unit content

In this specification bold text refers to higher tier only content. Italic text refers to practical investigations, which students are required to demonstrate an understanding of.

Topic 1

The building blocks of cells

1.1 Describe the function of the components of a bacterial cell including chromosomal DNA, plasmid DNA, flagella and cell wall

1.2 Describe the function of the components of a plant cell including chloroplast, large vacuole, cell wall, cell membrane, mitochondria, cytoplasm and nucleus

1.3 Describe the function of the components of an animal cell including cell membrane, mitochondria, cytoplasm and nucleus

1.4 Describe how plant and animal cells can be studied in greater detail with a light microscope

1.5 Demonstrate an understanding of how changes in microscope technology have enabled us to see cells with more clarity and detail than in the past, including simple magnification calculations

1.6 Recall that a gene is a section of a molecule of DNA and that it codes for a specific protein

1.7 Describe a DNA molecule as:

- two strands coiled to form a double helix

- strands linked by a series of complementary base pairs joined together by weak hydrogen bonds:

    i - adenine (A) with thymine (T)

    ii - cytosine (C) with guanine (G)

1.8 Investigate how to extract DNA from cells

1.9 Explain how the structure of DNA was discovered, including the roles of the scientists Watson, Crick, Franklin and Wilkins

1.10 Demonstrate an understanding of the implications of sequencing the human genome (Human Genome Project) and of the collaboration that took place within this project

1.11 Demonstrate an understanding of the process of genetic engineering, including the removal of a gene from the DNA of one organism and the insertion of that gene into the DNA of another organism

1.12 Discuss the advantages and disadvantages of genetic engineering to produce GM organisms, including:

- beta carotene in golden rice to reduce vitamin A deficiency in humans

- the production of human insulin by genetically modified bacteria

- the production of herbicide-resistant crop plants

Unit B2: The components of life

1.13 Describe the division of a cell by mitosis as the production of two daughter cells, each with identical sets of chromosomes in the nucleus to the parent cell, and that this results in the formation of two genetically identical diploid body cells

1.14 Recall that mitosis occurs during growth, repair and asexual reproduction

1.15 Recall that, at fertilisation, haploid gametes combine to form a diploid zygote

1.16 Describe the division of a cell by meiosis as the production of four daughter cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes

1.17 Recall that cloning is an example of asexual reproduction that produces genetically identical copies

1.18 Demonstrate an understanding of the stages in the production of cloned mammals, including:

- removal of diploid nucleus from a body cell

- enucleation of egg cell

- insertion of diploid nucleus into enucleated egg cell

- stimulation of the diploid nucleus to divide by mitosis

- implantation into surrogate mammals

1.19 Demonstrate an understanding of the advantages, disadvantages and risks of cloning mammals

1.20 Recall that stem cells in the embryo can differentiate into all other types of cells, but that cells lose this ability as the animal matures

1.21 Demonstrate an understanding of the advantages, disadvantages and risks arising from adult and embryonic stem cell research

1.22 Describe how the order of bases in a section of DNA decides the order of amino acids in the protein

1.23 Demonstrate an understanding of the stages of protein synthesis, including transcription and translation:

- the production of complementary mRNA strand in the nucleus

- the attachment of the mRNA to the ribosome

- the coding by triplets of bases (codons) in the mRNA for specific amino acids

- the transfer of amino acids to the ribosome by tRNA

- the linking of amino acids to form polypeptides

1.24 Describe each protein as having its own specific number and sequence of amino acids, resulting in different-shaped molecules that have different functions, including enzymes

1.25 Demonstrate an understanding of how gene mutations change the DNA base sequence and that mutations can be harmful, beneficial or neither

Unit B2: The components of life

1.26 Describe enzymes as biological catalysts

1.27 Demonstrate an understanding that enzymes catalyse chemical reactions occurring inside and outside living cells, including:

- DNA replication

- protein synthesis

- digestion

1.28 Describe the factors affecting enzyme action, including:

- temperature

- substrate concentration

- pH

1.29 Recall that enzymes are highly specific for their substrate

1.30 Demonstrate an understanding of the action of enzymes in terms of the ‘lock-and-key’ hypothesis

1.31 Describe how enzymes can be denatured due to changes in the shape of the active site

1.32 Investigate the factors that affect enzyme activity

Topic 2

Organisms and energy

2.1 Recall that respiration is a process used by all living organisms that releases the energy in organic molecules

2.2 Explain how the human circulatory system facilitates respiration, including:

- glucose and oxygen diffuses from capillaries into respiring cells

- carbon dioxide diffuses from respiring cells into capillaries

2.3 Define diffusion as the movement of particles from an area of high concentration to an area of lower concentration

2.4 Demonstrate an understanding of how aerobic respiration uses oxygen to release energy from glucose and how this process can be modelled using the word equation for aerobic respiration

2.5 Investigate the effect of exercise on breathing rate and heart rate

2.6 Explain why heart rate and breathing rate increase with exercise

2.7 Calculate heart rate, stroke volume and cardiac output, using the equation cardiac output 5 stroke volume 3 heart rate

2.8 Demonstrate an understanding of why, during vigorous exercise, muscle cells may not receive sufficient oxygen for their energy requirements and so start to respire anaerobically

2.9 Demonstrate an understanding of how anaerobic respiration releases energy from glucose and how this process can be modelled using the word equation for anaerobic respiration

2.10 Recall that the process of anaerobic respiration releases less energy than aerobic respiration

Unit B2: The components of life

2.11 Describe how a build-up of lactic acid requires extra oxygen to break it down. This is called excess post-exercise oxygen consumption or EPOC (formerly known as oxygen debt)

2.12 Explain why heart rate and breathing rate remain high after exercise

2.13 Describe how the structure of a leaf is adapted for photosynthesis, including:

- large surface area

- containing chlorophyll in chloroplasts to absorb light

- stomata for gas exchange (carbon dioxide, oxygen and water vapour)

2.14 Demonstrate an understanding of how photosynthesis uses light energy to produce glucose and how this process can be modelled using the word equation for photosynthesis

2.15 Demonstrate an understanding of how limiting factors affect the rate of photosynthesis, including:

- light intensity

- CO2 concentration

- temperature

2.16 Investigate how factors, including the effect of light intensity, CO2 concentration or temperature, affect the rate of photosynthesis

2.17 Explain how the loss of water vapour from leaves drives transpiration

2.18 Explain how water, glucose and mineral salts are transported through a plant, including:

- mineral uptake in roots by active transport

- the role of the xylem and phloem vessels

2.19 Describe how root hair cells are adapted to take up water by osmosis

2.20 Define osmosis as the movement of water molecules from an area of higher concentration of water to an area of lower concentration of water through a partially permeable membrane

2.21 Investigate osmosis

2.22 Investigate the relationship between organisms and their environment using fieldwork techniques

Unit B2: The components of life

2.23 Investigate the distribution of organisms in an ecosystem, using sampling techniques including:

- pooters

- sweep nets/pond nets

- pitfall traps

- quadrats

and measure environmental factors including:

- temperature

- light intensity

- pH

Topic 3

Common systems

3.1 Evaluate the evidence for evolution based on the fossil record

3.2 Explain why there are gaps in the fossil record, including:

- because fossils do not always form

- because soft tissue decays

- because many fossils are yet to be found

3.3 Explain how the anatomy of the pentadactyl limb provides scientists with evidence for evolution

3.4 Describe growth in terms of increase in size, length and mass

3.5 Interpret growth data in terms of percentile charts

3.6 Explain how cell division, elongation and differentiation contribute to the growth and development of a plant

3.7 Explain how cell division and differentiation contribute to the growth and development of an animal

3.8 Recall the structure and function of the following parts of the blood, including:

- red blood cells

- white blood cells

- plasma

- platelets

3.9 Describe the grouping of cells into tissues, tissues into organs, and organs into organ systems

Unit B2: The components of life

3.10 Explain how the structure of the heart is related to its function, including:

- the four major blood vessels associated with the heart (pulmonary artery, pulmonary vein, aorta, vena cava)

- left atrium and ventricle to pump oxygenated blood

- right atrium and ventricle to pump deoxygenated blood

- valves to prevent backflow (names not required)

- left ventricle has a thicker muscle wall than the right ventricle

- the direction of blood flow through the heart

3.11 Describe how the circulatory system transports substances around the body, including:

- arteries transport blood away from the heart

- veins transport blood to the heart

- capillaries exchange materials with tissues

3.12 Describe the functions of the parts of the digestive system, including:

- mouth

- oesophagus

- stomach

- small and large intestines

- pancreas

- liver

- gall bladder

3.13 Explain the role of the muscular wall of the alimentary canal in peristalsis

3.14 Explain the role of digestive enzymes, including:

- carbohydrases, including amylase, which digest starch to simple sugars

- proteases, including pepsin, which digest proteins to amino acids

- lipase, which digests fats to fatty acids and glycerol

3.15 Explain the role of bile in neutralising stomach acid and emulsifying fats

3.16 Explain how the structure of villi (large surface area, single layer of cells and capillary network) allows efficient absorption of the soluble products of digestion

3.17 Investigate the effect of different concentrations of digestive enzymes, using and evaluating models of the alimentary canal

Unit B2: The components of life

3.18 Evaluate the evidence for the claimed benefits of the use of functional foods as part of a healthy diet, including:

- probiotics containing Bifidobacteria and lactic acid bacteria Lactobacillus

- prebiotic oligosaccharides

- plant stanol esters