KS4 Cells

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KS4 Cells & Exchanges Learning Objectives

1.1.1 Eukaryotes and prokaryotes.

Students should

Know that Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.
Know that Bacterial cells (prokaryotic cells) are much smaller in comparison. They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one more small rings of DNA called plasmids.

1.1.2 Animal and plant cells

Students should:

Be able to explain how the main sub-cellular structures, including the nucleus, cell membranes, mitochondria, chloroplasts in plant cells and plasmids in bacterial cells are related to their functions.
Know that most animal cells have the following parts:
- a nucleus, which controls the activities of the cell
- cytoplasm, in which most of the chemical reactions take place
- a cell membrane, which controls the passage of substances into and out of the cell
- mitochondria, which is where aerobic respiration takes place
- ribosomes, which are where protein synthesis occurs.
Know that in addition to the parts found in animal cells, plant cells often have:
- chloroplasts, which absorb light to make food by photosynthesis
- a permanent vacuole filled with cell sap.
Know that plant and algal cells have a cell wall made of cellulose, which strengthens the cell.

1.1.2 Cell specialisation

Students should:

Be able to explain how the structure of different types of cell relate to their function in a tissue, an organ or organ system, or the whole organism.
Know examples of how cells may be specialised to carry out a particular function, including: sperm cells, nerve cells and muscle cells in animals and root hair cells, xylem and phloem cells in plants.

1.1.4 Cell Differentiation

Students should:

Know that as an organism develops, cells differentiate to form different types of cells.
Know that most types of animal cell differentiate at an early stage whereas many types of plant cells retain the ability to differentiate throughout life.
Know that in mature animals, cell division is mainly restricted to repair and replacement.
Know that as a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function - it has become a specialised cell.

1.1.5 Microscopy

Students should:

Know the definition of the terms magnification and resolution.
Know that an electron microscope has much higher magnification and resolving power than a light microscope.
Know that an electron microscope can be used to study cells in much finer detail and that this has enabled biologists to see and understand many more sub-cellular structures.

2.1 Principles of organisation

Students should:

Know that Cells are the basic building blocks of all living organisms.
Know that a Tissue is a group of cells with a similar structure and function.
Know that Organs are aggregations of tissues performing specific functions.
Know that Organs are organised into organ systems, which work together to form organisms.
Be able to develop an understanding of size and scale in relation to cells, tissues, organs and systems.

1.1.6 Culturing microorganisms

Students should:

Know that bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.
Know that bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate.
Know that uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.
Be able to describe and explain how to prepare an uncontaminated culture, including:
- Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms
- inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame
-the lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture, and stored upside down to stop condensation drops falling onto the agar surface.
In school and college laboratories, cultures should be incubated at a maximum temperature of 25 °C to reduce the likelihood of the growth of pathogens that might be harmful to humans.

1.3.1 Diffusion

Students should:

Know that substances may move into and out of cells across the cell membranes via diffusion.
Know that diffusion is the spreading of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
Know that some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.
Know and explain how different factors which the rate of diffusion, including:
- the difference in concentrations (concentration gradient)
- the temperature
- the surface area of the membrane.
Know that a single-celled organism has a relatively large surface area to volume ratio allowing sufficient transport of molecules into and out of the cell to meet the needs of the organism.
Explain the needs for exchange surfaces and a transport system in multicellular organisms in terms of surface area to volume ratio.
Be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials.
Know that in multicellular organisms the smaller surface area to volume ratio means surfaces and organ systems are specialised for exchanging materials to allow sufficient molecules to be transported into and out of cells for the organism’s needs.
Know how the effectiveness of an exchange surface is increased by:
- having a large surface area
- a membrane that is thin, to provide a short diffusion path
- (in animals) having an efficient blood supply
- (in animals, for gaseous exchange) being ventilated.
Be able to calculate and compare surface area to volume ratios.

1.3.2 Osmosis

Students should:

Know that water may move across cell membranes via osmosis.
Know that osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

1.3.3 Active transport

Students should:

Know that active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient).
Know that active transport requires energy from respiration.
Know that active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil and that plants require these ions for healthy growth.
Know that active transport allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration, which will then be used for cell respiration.
Be able to explain the differences between diffusion, osmosis and active transport.
Know how isotonic drinks and high energy drinks are used in sport.

Skills

Use prefixes centi, milli, micro and nano.
Demonstrate an understanding of the scale and size of cells and be able to make order of magnitude calculations, including the use of standard form.
Use prefixes centi, milli, micro and nano.
Carry out calculations involving magnification, real size and image size using the formula: magnification = size of image/size of real object
Students should be able to express answers in standard form if appropriate.
Calculate the number of bacteria in a population after a certain time if given the mean division time.
Calculate cross-sectional areas of colonies or clear areas around colonies using πr².
use simple compound measures of rate of water uptake
use percentiles
calculate percentage gain and loss of mass of plant tissue.
Students should be able to plot, draw and interpret appropriate graphs.