Lecture notes
Class notes for AQA GCSE Biology Higher
Includes simple but detailed notes on Cell Biology, Differentiation and Specialisation, and Microscopy to help revise for the upcoming exams.
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Lesson 1: Cell StructureAll living things are made up of basic units called cells. Within an organism, there are many distinct
cell types, each having unique subcellular structures that allow them to carry out their distinct
functions.
Prokaryotic vs Eukaryotic
➔ If a cell has a nucleus or not, it can be divided into two categories:
◆ Prokaryotic cells are defined as those lacking a nucleus, such as bacteria.
◆ Eukaryotic cells are those that have a nucleus, which include plant and animal cells.
➔ Compared to eukaryotic cells, prokaryotic cells are typically smaller and considerably simpler.
➔ Prokaryotic organisms are referred to as prokaryotes, whereas eukaryotic organisms are
composed of eukaryotic cells.
➔ Prokaryotes are often single-celled organisms, whereas eukaryotes are frequently
multicellular organisms composed of many cells.
Animal Cell Structure (Eukaryotic Cells)
➔ Nucleus:
◆ A nucleus that houses all of the genetic
material—including DNA—necessary
for directing the actions of the cell.
➔ Cytoplasm:
◆ Nutrient-rich jelly-like substance that is
made up of salts, enzymes, and other
elements needed for chemical
processes.
➔ Cell Membrane:
◆ Certain substances pass through its
structure whereas others do not. As so, it regulates the flow of materials into and
out of the cell.
➔ Mitochondria:
◆ Organelles that house the respiration-related enzymes and are the site of the
majority of energy release during respiration.
➔ Ribosomes:
◆ Where the production of protein synthesis takes place.
Plant Cell Structure (Eukaryotic Cells)
Animal cells and plant cells both have the same characteristics,
but plant cells also have:
➔ Cell Wall:
◆ Composed of cellulose fibres, which sustain and
strengthen the cell of the plant.
➔ Vacuole:
◆ Contains "cell sap," a mild fluid of sugar and salts
that keeps the cell inflated (swollen).
➔ Chloroplasts:
◆ Organelles that hold chlorophyll, a green pigment
used in photosynthesis to absorb light energy. Has
the enzymes required for photosynthesis present.
, Bacteria Cell Structure (Prokaryotes)
➔ Bacteria are prokaryotic, meaning
they lack a nucleus, therefore their
genetic material is free to roam
around in the cytoplasm. They
contain a primary circular DNA
strand as well as occasional
accessory little DNA rings known
as plasmids.
➔ Although they lack mitochondria
and chloroplasts, bacteria do have
cytoplasm, a cell wall, and a cell
membrane.
➔ Flagella are structures resembling hairs that aid in the movement of germs.
Comparing cell types
Eukaryotic cell Prokaryotic cell
Size 5 μm - 100 μm 0.2 μm - 20 μm
Outer layers of cell In fungi and plants, the cell The cell wall encloses the
wall encloses the cell membrane.
membrane.
Cell contents Cytoplasm,plant chloroplasts, Ribosomes, cytoplasm
ribosomes, and mitochondria ● absence of
are examples of cell organelles. mitochondria and
chloroplasts
Genetic material A few basic eukaryotic species Additional DNA is located on
have plasmids, which are DNA one or more rings known as
contained in their nuclei. plasmids. DNA is a single
molecule that is found freely
in the cytoplasm.
Type of cell division Mitosis Binary fission
Lesson 2: Differentiation and Specialisation
The process of differentiation is how various cell types acquire their unique cell architectures and
become specialised.
Differentiation
➔ A cell must first generate the appropriate subcellular structures for the job before it can
perform its particular function within an organism. It creates specialised cells through a
process known as differentiation.
➔ In animal cells, differentiation occurs mostly during the early stages of the organism's
development; in contrast, most plants retain the capacity to differentiate throughout their
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