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Biology – Unit 2: Section 1 – Cells
Cells and organelles
Structure and function of organelles
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Nucleus
o Large organelle surrounded by a nuclear envelop (double membrane) which has pores
o Contains chromatin and a nucleolus
o Chromatin is made from proteins and DNA
o Pores allows substances to move in and out of the nucleus and into the cytoplasm
o The nucleolus makes ribosomes
Lysosomes
o Round organelle surrounded by a membrane
o Contains digestive enzymes that digest invading cells or break down worn out components of
the cell
Vesicle
o Small fluid-filled sac in the cytoplasm surrounded by a membrane
o Transports substances in and out of the cell
o Some are formed at the Golgi apparatus or the endoplasmic reticulum or the cell surface
Ribosome
o Very small organelle that floats free in the cytoplasm or is attached to the rough endoplasmic
reticulum
o Where proteins are made
Rough endoplasmic reticulum (rER)
o Membranes enclosed in a fluid-filled space which is covered in ribosomes
o Folds and processes proteins made at the ribosomes
Smooth endoplasmic reticulum (sER)
o Membranes enclosed in a fluid-filled space
o Synthesises and processes lipids
Golgi apparatus
o Fluid-filled flatted sacs, vesicles are often seen at the edges
o Processes and packages new lipids and proteins
o Makes lysosomes
Centriole
o Hollow cylinders containing a ring of microtubules
o Involved with the separation of chromosomes during cell division
Mitochondrion
o Oval shape, with a double membrane, the inner membrane is folded to form structures
called cristae
o Inside is the matrix which contains enzymes involved in respiration
o Site of aerobic respiration and where ATP energy is produced

Prokaryotic cells
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DNA in no nucleus
Cell membrane
Cell wall
Plasmid (ring of DNA)

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Ribosomes
Flagellum (tail used to propel the cell)

Eukaryotic
Larger cells 10-100µm
DNA is linear
Nucleus present – DNA inside nucleus
No cell wall (animals) cellulose (plants) chitin (fungi)
Many organelles, mitochondria present
Large ribosomes

Prokaryotic
Extremely small less than 2
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2
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4
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2
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4
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What is the function of the nucleolus?
To create ribosomes
Which organelle contain digestive enzymes?
Lysosome
How does the structure of rER differ from that of sER?
rER contains ribosomes attached to it whereas sER doesn’t
Give two difference between prokaryotic cells and eukaryotic
Eukaryotic cells contain mitochondria whereas prokaryotic cells doesn’t, eukaryotic cells also contain
a nucleus whereas in prokaryotic cells the DNA floats free
Identify these two organelles from their description
a
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The inner membrane is folded
and projects into the inner space, which is filled with grainy material
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A collection of flattened membrane ‘sacs’ arranged roughly parallel to one another
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2
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Discuss whether the liver is best
described as a tissue or organ
An organ because it is made of a number of different tissues formed by similar cells

The cell cycle and mitosis
The cell cycle
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3
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Mitosis
o When a cell divides into two identical cells
Gap phase 1
o Cell grows and new organelles and proteins are made
Synthesis
o Cell replicates its DNA, ready to divide by mitosis
Gap phase 2
o Cell keeps growing and proteins needed for cell division are made

Mitosis
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Needed for growth and repairing damaged tissue
Some organisms produce asexually using mitosis

Division stages
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3
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5
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2
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4
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6
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8
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2
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4
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For each of the cells A, B and C state the stage of mitosis, giving a reason for your answer
A is metaphase because they are lined up along the equator, B is Telophase because the two
cells are separating and the nuclear envelop are forming again and C is Anaphase as the
chromatids are being separated by their centromere
b

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