Unit 2: Cells, Development, Biodiversity and Conservation

3.1Cells as the basis of life

Know that all living organisms are made of cells, sharing some common features

3.2Organisation in multicellular organisms

Understand how the cells of multicellular organisms are organised into tissues, tissues into organs, and organs into organ systems

3.3Eukaryotic cell ultrastructure

(i) know the ultrastructure of eukaryotic cells, including nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes and Golgi apparatus (ii) understand the function of the organelles listed in (i)

3.4rER, Golgi apparatus and protein transport

Understand the role of the rough endoplasmic reticulum (rER) and the Golgi apparatus in protein transport within cells, including their role in the formation of extracellular enzymes

3.5Prokaryotic cell ultrastructure

(i) know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes and circular DNA (ii) understand the function of the structures listed in (i)

3.6Recognising organelles in EM images

Be able to recognise the organelles in 3.3 from electron microscope (EM) images

3.7Microscopy magnification, resolution and staining

(i) know how magnification and resolution can be achieved using light and electron microscopy (ii) understand the importance of staining specimens in microscopy

3.8Core Practical 5 - animal cells and scale

CORE PRACTICAL 5 (i) use a light microscope to make observations and labelled drawings of suitable animal cells (ii) use a graticule with a microscope to make measurements and understand the concept of scale

3.9Loci and gene linkage

(i) know that a locus is the location of genes on a chromosome (ii) understand the linkage of genes on a chromosome

3.10Meiosis and genetic variation

Understand the role of meiosis in ensuring genetic variation through the production of non-identical gametes as a consequence of independent assortment of chromosomes in metaphase I and crossing over of alleles between chromatids in prophase I Names of the stages of prophase are not required.

3.11Mammalian gamete specialisation

Understand how mammalian gametes are specialised for their functions (including the acrosome in sperm and the zona pellucida in the egg cell)

3.12Mammalian fertilisation

Know the process of fertilisation in mammals, including the acrosome reaction, the cortical reaction and the fusion of nuclei

3.13Fertilisation in flowering plants

Know the process of fertilisation in flowering plants, starting with the growth of a pollen tube and ending with the fusion of nuclei

3.14Mitosis and the cell cycle

Understand the role of mitosis and the cell cycle in producing genetically identical daughter cells for growth and asexual reproduction

3.15Core Practical 6 - root tip squash mitosis

CORE PRACTICAL 6 Prepare and stain a root tip squash to observe the stages of mitosis.

3.16Mitotic index calculations

Be able to calculate mitotic indices

3.17Stem cells and medical therapies

(i) understand what is meant by the terms stem cell, pluripotent and totipotent, morula and blastocyst (ii) be able to discuss the ways in which society uses scientific knowledge to make decisions about the use of stem cells in medical therapies

3.18Differential gene expression and cell specialisation

Understand how cells become specialised through differential gene expression, producing active mRNA, leading to the synthesis of proteins which, in turn, control cell processes or determine cell structure in animals and plants

3.19Post-transcriptional changes to mRNA

Understand how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA (mRNA)

3.20Phenotype, environment and epigenetics

(i) understand how phenotype is the result of an interaction between genotype and the environment (ii) know how epigenetic modification, including DNA methylation and histone modification, can alter the activation of certain genes (iii) understand how epigenetic modifications can be passed on following cell division

3.21Multiple alleles, polygenic inheritance and continuous variation

Understand how some phenotypes are affected by multiple alleles for the same gene, or by polygenic inheritance, as well as the environment, and how polygenic inheritance can give rise to phenotypes that show continuous variation

(i) know the structure and ultrastructure of plant cells including cell wall, chloroplast, amyloplast, vacuole, tonoplast, plasmodesmata, pits and middle lamella and be able to compare it with animal cells (ii) understand the function of the structures listed in (i)

Be able to recognise the organelles in 4.1 from electron microscope (EM) images

Understand the structure and function of the polysaccharides starch and cellulose, including the role of hydrogen bonds between the β-glucose molecules in the formation of cellulose microfibrils

Understand how the arrangement of cellulose microfibrils and secondary thickening in plant cell walls contributes to the physical properties of xylem vessels and sclerenchyma fibres in plant fibres that can be exploited by humans

Know the similarities and differences between the structures of, the position in the stem, and the function of sclerenchyma fibres (support), xylem vessels (support and transport of water and mineral ions) and phloem (translocation of organic solutes)

CORE PRACTICAL 7 Use a light microscope to: (i) make observations, draw and label plan diagrams of transverse sections of roots, stems and leaves (ii) make observations, draw and label cells of plant tissues (iii) identify sclerenchyma fibres, phloem, sieve tubes and xylem vessels and their location.

Understand how the uses of plant fibres and starch may contribute to sustainability, including plant-based products to replace oil-based plastics

Understand the importance of water and inorganic ions (nitrate, calcium ions and magnesium ions) to plants

CORE PRACTICAL 8 Determine the tensile strength of plant fibres.

Understand the conditions required for bacterial growth

Know that substances derived from plants can have antimicrobial and other therapeutic properties

CORE PRACTICAL 9 Investigate the antimicrobial properties of plants, including aseptic techniques for the safe handling of bacteria.

Understand the development of drug testing from historic to contemporary protocols, including William Withering’s digitalis soup, double blind trials, placebo and three-phased testing

(i) understand that classification is a means of organising the variety of life based on relationships between organisms using differences and similarities in phenotypes and in genotypes, and is built around the species concept (ii) understand the process and importance of critical evaluation of new data by the scientific community leading to new taxonomic groupings, based on molecular evidence, including the three-domain system (Archaea, Bacteria and Eukarya)

Know that, over time, the variety of life has become extensive but is now being threatened by human activity

Understand what is meant by the terms biodiversity and endemism

Know how biodiversity can be measured within a habitat using species richness, and within a species using genetic diversity by calculating the heterozygosity index: number of heterozygotes heterozygosity index = number of individuals in the population

Understand how biodiversity can be compared in different habitats using the formula to calculate an index of diversity (D): N (N-1) D= Σn (n-1)

Understand the concept of niche and be able to discuss examples of adaptations of organisms to their environment (behavioural, anatomical and physiological)

(i) understand how the Hardy-Weinberg equation can be used to see whether a change in allele frequency is occurring in a population over time (ii) understand that changes in allele frequency can come about as a result of mutation and natural selection (iii) understand that reproductive isolation can lead to accumulation of different genetic information in populations, potentially leading to the formation of new species

Be able to evaluate the methods used by zoos and seed banks in the conservation of endangered species and their genetic diversity, including scientific research, captive breeding programmes, reintroduction programmes and education