1.
State what is meant by a eukaryotic cell.
[1 mark]
- a cell with a nucleus / membrane-bound organelles
JD SCIENCE
Key concepts in biology
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by a prokaryotic cell.
[1 mark]
- a cell with no nucleus, DNA free in the cytoplasm
3.
State what is meant by the nucleus.
[1 mark]
- organelle that contains DNA / controls the cell
4.
State what is meant by the cell membrane.
[1 mark]
- partially permeable barrier around the cell
5.
State what is meant by a chloroplast.
[1 mark]
- organelle where photosynthesis occurs
6.
State what is meant by diffusion.
[1 mark]
- net movement of particles from high to low concentration
7.
State what is meant by osmosis.
[1 mark]
- net movement of water from dilute to concentrated solution through a partially permeable membrane
8.
State what is meant by active transport.
[1 mark]
- movement against a concentration gradient using energy
9.
State what is meant by mitosis.
[1 mark]
- cell division producing two genetically identical diploid cells
10.
State what is meant by a stem cell.
[1 mark]
- an undifferentiated cell that can divide and specialise
11.
Devon is asked about a eukaryotic cell in a Edexcel Biology paper.
(a) [2 marks]
- has nucleus, mitochondria, cytoplasm, cell membrane
(b) [3 marks]
- why muscle cells contain many mitochondria
12.
Devon is asked about a prokaryotic cell in a Edexcel Biology paper.
(a) [2 marks]
- has cell wall, chromosomal DNA, plasmids, flagella
(b) [3 marks]
- why bacteria can transfer plasmids
13.
Devon is asked about the nucleus in a Edexcel Biology paper.
(a) [2 marks]
- surrounded by a nuclear membrane, contains chromosomes
(b) [3 marks]
- why a red blood cell has no nucleus when mature
14.
Devon is asked about the cell membrane in a Edexcel Biology paper.
(a) [2 marks]
- controls what enters and leaves
(b) [3 marks]
- why osmosis needs a partially permeable membrane
15.
Devon is asked about a chloroplast in a Edexcel Biology paper.
(a) [2 marks]
- contains chlorophyll and membranes
(b) [3 marks]
- why root hair cells have no chloroplasts
16.
Devon is asked about diffusion in a Edexcel Biology paper.
(a) [2 marks]
- passive, no energy from respiration
(b) [3 marks]
- why gas exchange uses diffusion
17.
A cell image is 9 mm across. The actual cell is 0.02 mm. Calculate the magnification.
[3 marks]
- magnification = image size ÷ actual size
- Final answer: 450
18.
Magnification is ×450. The image is 20 mm. Calculate the actual size in µm.
[3 marks]
- actual = image ÷ mag; 1 mm = 1000 µm
- Final answer: 44.44 µm
19.
A cube cell of side 3 mm has what surface area to volume ratio?
[3 marks]
- SA = 6a², V = a³
- Final answer: 2 : 1
20.
A microscope uses a ×10 eyepiece and a ×50 objective. What is the total magnification?
[3 marks]
- multiply the two lenses
- Final answer: ×500
21.
Devon counts 24 cells in a 0.004 mm³ haemocytometer square. Estimate the number of cells in 1 mm³.
[3 marks]
- scale up
- Final answer: 6000
22.
A cell divides by mitosis every 2 hours. Starting from 1 cell, how many cells after 8 hours?
[3 marks]
- 4 divisions, 2⁴
- Final answer: 16
23.
Devon carries out the microscopy required practical to view onion epidermis. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: not always applicable / stain used
- Dependent: clarity of organelles seen
(b) [2 marks]
- same light intensity / same stain time
- so the test is fair / only one variable is changed
(c) [2 marks]
- cells overlapping
- count only single-layer cells
24.
Devon carries out the osmosis required practical with potato cylinders. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: concentration of sugar solution
- Dependent: change in mass / length
(b) [2 marks]
- same temperature, same start length, blot dry
- so the test is fair / only one variable is changed
(c) [2 marks]
- surface water left on the potato changes mass
25.
Devon carries out an investigation of diffusion in agar cubes with indicator. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: cube size / concentration
- Dependent: time for colour to disappear
(b) [2 marks]
- same temperature
- so the test is fair / only one variable is changed
(c) [2 marks]
- cubes not identical size
26.
Devon carries out preparing a cheek-cell slide. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: n/a
- Dependent: quality of the image
(b) [2 marks]
- thin layer of cells
- so the test is fair / only one variable is changed
(c) [2 marks]
- too many cells / air bubbles
27.
Compare diffusion with active transport.
[4 marks]
- diffusion is down the gradient / passive
- active transport is against the gradient / needs ATP
28.
Compare animal cells with plant cells.
[4 marks]
- both have nucleus, cytoplasm, membrane, mitochondria
- only plant cells have cell wall, chloroplasts, permanent vacuole
29.
Compare mitosis with meiosis.
[4 marks]
- mitosis: two identical diploid cells
- meiosis: four haploid genetically different cells
30.
Compare embryonic stem cells with adult stem cells.
[4 marks]
- embryonic can become most cell types
- adult are more limited / fewer ethical issues
31.
Apply your knowledge of osmosis to this situation: water leaves the cells
[3 marks]
- water leaves the cells
32.
Apply your knowledge of active transport to this situation: soil concentration is lower than inside the cell
[3 marks]
- soil concentration is lower than inside the cell