Hi,
I achieved all 9s in my 2022 GCSE exams. I achieved 239/252 in Geography, 172/200 in Biology, 192/200 in Chemistry and 189/200 in Physics. These notes were my main source of revision to achieve these grades, I hope they're useful. Disclaimer: due to covid and Advance Information, a small mino...
May/June 2022
GCSE Biology Notes
For each topic:
- Freesciencelessons video + Cognito video with notes
- Key Cards
- After each large topic, exampro questions, save my exams digital, and CGP practice
PAPER I
Eukaryotes and Prokaryotes
• Both animals and plants are eukaryotes
• All eukaryotic cells have DNA enclosed in a nucleus
• In fact, that is the definition of a eukaryotic cell: a cell that contains its genetic
material (i.e., DNA) enclosed in a nucleus
• Plant and animal (eukaryotic) cells also have a cell membrane and a cytoplasm
• Unlike animals and plants, bacteria are prokaryotes
• In prokaryotic cells, the genetic material is not enclosed in a nucleus, instead it is
looped freely in the cytoplasm:
,Major topic Low-stakes topic
• Another difference between prokaryotic and eukaryotic cells is that prokaryotic
cells are much smaller than eukaryotic cells (you can remember that because
bacteria are really small)
• Prokaryotes (like bacteria) may also have small rings of DNA called plasmids
which encode for a certain characteristic
• Like eukaryotes, prokaryotic cells have a cell membrane but they also have a cell
wall (note: this is not a cellulose cell wall like the eukaryotic cell wall of a plant)
• Note: prokaryotes are prokaryotic cells because almost all prokaryotes are
unicellular
• Bacteria have ribosomes but do not have mitochondria or chloroplasts
Animal and Plant Cells
• Here is an animal cell:
• The nucleus holds all the genetic material of the cell, controlling the activities of
that cell
• The cytoplasm is a gel-like solution where metabolic chemical reactions take
place
• The cell membrane controls what enters and leaves the cell
• Mitochondria are tiny organelles where aerobic respiration takes place to release
energy for the cell’s reactions
• Ribosomes are the sites of protein synthesis
• The mitochondria are tiny but the ribosomes are even smaller (that is how you
distinguish them in a diagram)
,Major topic Low-stakes topic
• Here is a plant cell:
• EVERYTHING an animal cell has, a plant/algal cell has
• Hence, plant cells also have a cell membrane, a nucleus, a cytoplasm,
mitochondria and ribosomes
• But they also have a few extra subcellular structures:
• They have chloroplasts which are organelles that contain chlorophyll to absorb
light energy needed for photosynthesis – hence, this is where photosynthesis
takes place
• They have a cellulose cell wall that strengthens the cell
• They also have a permanent vacuole filled with cell sap which helps keep the
plant turgid and rigid
, Major topic Low-stakes topic
Cell specialisation
• Most animal cells are specialised so have adaptations that help them to carry out
a particular function
• When cells become specialised, differentiation takes place
• The 3 different specialised animal cells you need to be able to explain
adaptations for are sperm cells, nerve cells and muscle cells:
• (1) Sperm cells
• The role of a sperm cell is to fertilise an egg
• One adaptation is that they contain only half the genetic material of a normal
adult cell, meaning that, when fertilisation takes place they produce a normal
body cell
• They also have a long tail that allows them to swim to the egg and fertilise it
• They have an acrosome which contains enzymes that allow it to digest through
the outer layer and cell membrane of the egg and fertilise it
• They have many mitochondria which provide energy for it to swim via aerobic
respiration
• (2) Nerve cells
• The role of a nerve cell is to carry electrical impulses around the body
• They have a long axon which allows it to carry impulses from one part of the
body to another along long distances
• The axons are covered in myelin which insulates the axon and speeds up
transmission of nerve impulses
• They also have synapses which are junctions that allow it to connect to other
nerve cells and carry the impulse from one cell to another
• Dendrites increase the surface area of the cell so other nerve cells can connect to
it
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