Cambridge (CIE) AS Your notes
Biology
Cells as the Basic Units of Living
Organisms
Contents
Eukaryotic Cell Structures & Functions
Animal & Plant Cells
The Vital Role of ATP
Prokaryotic v Eukaryotic Cells
Viruses
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, Eukaryotic Cell Structures & Functions
Your notes
Eukaryotic Cell Structures & Functions
Cells can be divided into two broad types; eukaryotic and prokaryotic cells
Eukaryotic cells have a more complex ultrastructure than prokaryotic cells
The term ultrastructure refers to the internal structure of cells
The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments
called organelles
Cell organelles
Cell surface membrane
All cells are surrounded by a cell surface membrane which separates the inside of cells
from their surroundings
Cell surface membranes controls the exchange of materials between the internal cell
environment and the external environment
The membrane is described as being partially permeable as it allows the passage of
some substances and not others
The cell membrane is formed from a phospholipid bilayer and spans a diameter of
around 10 nm
Cell surface membrane diagram
Cell surface membranes separate cell contents from the surrounding environment and
control the passage of substances into and out of cells
Nucleus
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, Present in all eukaryotic cells, the nucleus is a large organelle that is separated from the
cytoplasm by a double membrane
Your notes
The nucleus contains the DNA, which is arranged into chromosomes
Chromosomes contain DNA and proteins, which are collectively referred to as
chromatin
The nuclear membrane is known as the nuclear envelope, and contains many pores
Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of
the nucleus, as well as allowing enzymes and signalling molecules to move in
The nucleus contains a region known as the nucleolus, which is the site of ribosome
production
Nucleus diagram
The nucleus of a cell contains the genetic material
Rough & smooth endoplasmic reticulum
The endoplasmic reticulum (ER) is made up of a series of membranes that form flattened
sacs within the cell cytoplasm
The ER is linked with the nuclear envelope
There are two distinct types of ER, with different roles within the cell
The rough endoplasmic reticulum (RER)
Continuous folds of membrane that are linked with the nuclear envelope
The surface of the RER is covered in ribosomes
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Biology
Cells as the Basic Units of Living
Organisms
Contents
Eukaryotic Cell Structures & Functions
Animal & Plant Cells
The Vital Role of ATP
Prokaryotic v Eukaryotic Cells
Viruses
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, Eukaryotic Cell Structures & Functions
Your notes
Eukaryotic Cell Structures & Functions
Cells can be divided into two broad types; eukaryotic and prokaryotic cells
Eukaryotic cells have a more complex ultrastructure than prokaryotic cells
The term ultrastructure refers to the internal structure of cells
The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments
called organelles
Cell organelles
Cell surface membrane
All cells are surrounded by a cell surface membrane which separates the inside of cells
from their surroundings
Cell surface membranes controls the exchange of materials between the internal cell
environment and the external environment
The membrane is described as being partially permeable as it allows the passage of
some substances and not others
The cell membrane is formed from a phospholipid bilayer and spans a diameter of
around 10 nm
Cell surface membrane diagram
Cell surface membranes separate cell contents from the surrounding environment and
control the passage of substances into and out of cells
Nucleus
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 2
, Present in all eukaryotic cells, the nucleus is a large organelle that is separated from the
cytoplasm by a double membrane
Your notes
The nucleus contains the DNA, which is arranged into chromosomes
Chromosomes contain DNA and proteins, which are collectively referred to as
chromatin
The nuclear membrane is known as the nuclear envelope, and contains many pores
Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of
the nucleus, as well as allowing enzymes and signalling molecules to move in
The nucleus contains a region known as the nucleolus, which is the site of ribosome
production
Nucleus diagram
The nucleus of a cell contains the genetic material
Rough & smooth endoplasmic reticulum
The endoplasmic reticulum (ER) is made up of a series of membranes that form flattened
sacs within the cell cytoplasm
The ER is linked with the nuclear envelope
There are two distinct types of ER, with different roles within the cell
The rough endoplasmic reticulum (RER)
Continuous folds of membrane that are linked with the nuclear envelope
The surface of the RER is covered in ribosomes
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 3
