FET PHASE OXFORD SUCCESSFUL
LIFE SCIENCES OUP SA
Oxford Successful Life Sciences is a popular series. It includes: updated assessments according to the DBE’s 2017 Strengthening the CAPS circular
age-appropriate easy to understand language worked out planning tools that are photocopiable exam support built into every activity revision, practice tests and exams assessment guidance an exam section, packed with exam tips and practice papers a free resource CD, packed with useful teacher resources, with your Grade 11 and 12 Teacher’s Guide.
Successful OXFORD
Life Sciences LEARNER’S BOOK
K 11 I
GRADE 10 *Learner’s Book
*Teacher’s Guide *Leerdersboek
*Onderwysersgids
GRADE 11 *Learner’s Book
Teacher’s Guide Leerdersboek
Onderwysersgids
GRADE 12 *Learner’s Book
Teacher’s Guide
978 0 19 905743 6 978 0 19 905602 6 978 0 19 905857 0 978 0 19 599495 7
978 0 19 599509 1 978 0 19 599619 7 978 0 19 905434 3 978 0 19 904983 7
978 0 19 905268 4 978 0 19 905012 3
*The full list of e-pdf titles is available in the price list.
Life Sciences CORE CLASSROOM COURSE
CAPS UPDATED
Assessment Guidelines 2017
W. Bezuidenhout A. Clark S. Copley R. Engelbrecht
Oxford Successful Life Sciences Grade 11 Learner’s Book Secondary Catalogue 53
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FET PHASE
UNIT 7
Immunity
In this unit you will learn about: the immune response of plants and animals against infecting micro-organisms
vaccinations.
Pathogens are organisms that can cause disease. When foreign substances invade plant or animal bodies, an immune response is triggered. An immune response is the reaction of the body to potentially dangerous substances, especially disease-causing micro-organisms. Immunity is the protection of an organism against infection.
Defence mechanisms and immune responses in plants
Pathogenic bacteria can enter plants through pores in the leaves (stomata or hydathodes). They can also gain access through wounds created by nematodes or aphids that feed by inserting a stylet directly into a plant cell. Fungi can enter plant cells directly or extend hyphae on top of, between, or through plant cells.
Plants have active or passive defence mechanisms to protect them against diseases.
Passive defences
Passive defence in plants can be physical, structural or chemical. The epidermal layer covering the plant’s surface is the first defence mechanism. Plants produce various chemicals to destroy and prevent the spread of pathogens.
hairs on leaf deter pathogens thorns on plant surface deter grazers
thick, waxy cuticle forms a barrier against the degrading enzymes used to gain entry to the host
a thick cell wall reduces the ability of a pathogen to invade the plant
Figure 1 Passive physical defences in plants the stoma opening could be a point of entry for pathogens,
and plants may use hairs to guard this opening 22 Topic 1 Biodiversity and classification of micro-organisms c
9780195995091_OS_LS_11_LB.indb 22
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Nitrogen fixing
Nitrogen is a key component of amino acids that form proteins. Amino acids are important organic compounds that are structural components of cell membranes, enzymes and nucleic acids. Atmospheric nitrogen is unavailable to living organisms. Bacteria play an important role in cycling nitrogen between the atmosphere, plants, animals and soil: Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia that can be used by plants and animals.
During decomposition, bacteria break down organic material into ammonia.
Nitrifying bacteria such as Nitrosomonas and Nitrobacter convert ammonia to nitrites and nitrates in the presence of oxygen.
Denitrifying bacteria convert nitrates back into nitrogen gas, which is released into the atmosphere.
Symbiotic relationships with animals and plants
Microbes form beneficial mutualistic associations with multicellular organisms, including insects, invertebrates, fish, animals and plants. Two examples are given below: Bacteria live in the intestines of animals and insects to help them to digest nutrients. They also produce vitamins and growth factors. In humans, the bacterium Escherichia coli suppresses the growth of harmful bacteria (see Figure 2) and produces biotin and vitamin K.
Some nitrogen-fixing bacteria are free-living in soil and aquatic habitats. Other bacteria fix nitrogen in symbiotic associations with plants. The bacteria live in nodules on the roots of leguminous plants such as peas and beans. The plant obtains nitrogen from the bacteria and the bacterium receives a place to grow and obtains sugars from the plant. One such bacterium is Rhizobium (see Figure 3).
Activity
Figure 2 Light micrograph of Escherichia coli living in the large intestine of humans
Figure 3 Root nodules on leguminous plants that contain the bacteria Rhizobium
New words
Discuss the impact of micro-organisms on food webs and ecosystem balance
Discuss why you agree/disagree with the following statement: “Micro-organisms are small organisms and so have a relatively small impact on food webs and ecosystem balance.”
[10]
mutualistic: symbiotic relationship between two organisms where both organisms benefit from the relationship
symbiotic: living relationship between two organisms where at least one organism benefits
Unit 6 Role of micro-organisms in maintaining balance in the environment 21 2012/10/05 10:38 AM
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