Organelles divide the work of the cell. The nucleus holds the instructions. Mitochondria release energy. Ribosomes build proteins.
The idea
An animal cell and a plant cell both have a cell membrane, cytoplasm and a nucleus. The nucleus contains the chromosomes, which carry the genes. Ribosomes, some free in the cytoplasm and some on membranes, assemble proteins. Mitochondria are where aerobic respiration releases energy from food. The cell membrane is partially permeable and controls what enters and leaves. These parts are worth naming with their jobs, not as a list of labels.
A plant cell adds a cellulose cell wall outside the membrane, a large permanent vacuole containing cell sap, and chloroplasts in the cells that photosynthesise. The wall is freely permeable and gives support. The vacuole keeps the cell firm when it is full. Chloroplasts hold chlorophyll and are the site of photosynthesis. They are not in root cells. Mitochondria and chloroplasts do different energy jobs. Do not swap respiration and photosynthesis.
What earns the marks
Function marks require the job, not a second name for the organelle. "The mitochondrion is the powerhouse" is too vague unless you add that aerobic respiration happens there. Partially permeable is the membrane. Freely permeable is the wall. Chloroplasts are for photosynthesis. Mitochondria are for respiration. A drawing question, if you meet one in class, needs labels you can point to. This page uses words.
Practice questions
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
1Question 1
4 marks
State the function of each of the following.
(a) Nucleus (1 mark)
(b) Mitochondrion (2 marks)
(c) Ribosome (1 mark)
Model answer
(a) It controls the cell and contains the genetic material.
(b) It is the site of aerobic respiration, which releases energy.
(c) It is the site of protein synthesis.
Mark scheme
Controls the cell, or contains the chromosomes or genes1 mark
Site of aerobic respiration1 mark
Releases energy from food1 mark
Protein synthesis, or assembling proteins1 mark
2Question 2
2 marks
Give two differences between a palisade cell in a leaf and a cell in the root cortex. (2 marks)
Model answer
The palisade cell has chloroplasts and photosynthesises. The root cortex cell has no chloroplasts and does not photosynthesise. Both have a cell wall.
Mark scheme
Chloroplasts present in the palisade cell and absent in the root cell1 mark
Photosynthesis occurs in the palisade cell and not in the root cell. A correct second difference, such as more regular packing in the palisade, is also accepted if chloroplasts were already used1 mark
3Question 3
2 marks
A candidate wrote that mitochondria carry out photosynthesis. Explain why that is wrong, and name the organelle that does. (2 marks)
Model answer
Mitochondria carry out aerobic respiration. Photosynthesis is carried out in chloroplasts.
Mark scheme
Mitochondria are for respiration, not photosynthesis1 mark
Chloroplasts1 mark
Practise Biology with Anna
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
They are the site of aerobic respiration. Food is broken down with oxygen and energy is released for the cell. They do not photosynthesise. Chloroplasts do that.
Which plant cells lack chloroplasts?+
Cells that are not green, such as root cortex cells. They still have a nucleus, a membrane, a wall and mitochondria. They import sugar made in the leaves. They do not make it. All WASSCE Biology past questions