Edexcel Combined Biology Paper 1:
**NOT A SUMMARY, THIS IS IN COMPLETE DETAIL**
I attained 99 in Combined Science solely through this self made resource of mine. I have
painstakingly gathered information from every EDEXCEL specific resource I could lay my
hands on (including seneca, pmt, savemyexams, lit every single video on each topic i could
find and the EDEXCEL textbook itself) in order to create this incredibly precise document. It
meets every single specification point in meticulous detail, including diagrams and lengthy
explanations where needed. It is the boiling pot of absolutely every single thing you need to
know, nothing more n nothing less, to seize your 99 in GCSE Combined Science.
Key:
- Boldened: Specification point itself
Unit 1: Key concepts in biology in Paper 1 and Paper 2
1.1 Explain how the subcellular structures of eukaryotic cells and prokaryotic cells are related to their
functions, including:
A animals – nucleus, cell membrane, mitochondria and ribosomes
B plant cells – nucleus, cell membrane, cell wall, chloroplasts, mitochondria, vacuole and ribosomes
C bacteria – chromosomal DNA, plasmid DNA, cell membrane, ribosomes and flagella
There are two different type of cells:
> Eukaryotic: These are cells that contain a nucleus. Animals, plants and protists (single-celled organisms) are
eukaryotic organisms, protists. These can be both multicellular or single-celled.
> Prokaryotic: These are cells that do NOT contain a nucleus, instead their nuclear material is found floating in
the cytoplasm. These are always single-celled. Bacteria are prokaryotic organisms.
Organelles/sub-cellular structures present in BOTH animals and plants:
> Nucleus: Contains the DNA coding for a particular protein needed to build new cells. It is enclosed in a nuclear
membrane and controls the activities of the cell.
> Cytoplasm: Jelly-like fluid substance in which chemical reactions occur. It contains enzymes and organelles are
found in it.
> Cell membrane: It is selectively permeable, it controls substances entering and leaving the cell.
> Mitochondria: Where aerobic respiration reactions occur to provide energy for the cell
> Ribosomes: Where protein synthesis occurs. It is found on a structure called the “rough endoplasmic
reticulum”.
Organelles/sub-cellular structures present ONLY in PLANTS:
> Chloroplasts: Where photosynthesis takes place, to provide food for the plant. It contains the green chlorophyll
pigment which harvests the light needed for photosynthesis.
> Permanent vacuole: It contains cell sap which is a mixture of sugars, salts and water. It is used for storage and
is enclosed in a membrane (a wall that substances can pass through). It also supports the shape of the cell.
> Cell wall (also present in algal cells): Made from cellulose (a polymer of glucose), it increases the structural
strength of the cell.
Organelles/sub-cellular structures present in BACTERIA:
> Cytoplasm: Jelly-like fluid substance in which chemical reactions occur. It contains enzymes and organelles are
found in it.
> Cell membrane: It is selectively permeable, it controls substances entering and leaving the cell.
> Ribosomes: Where protein synthesis occurs.
> Chromosomal DNA: As bacteria have no nucleus because they are prokaryotic, the DNA floats in the
cytoplasm instead.
> Plasmids: Small rings of DNA that code for extra genes
,> Flagella: Long, thin “whip-like” tails attached to bacteria that allow them to move with a "cork-screw like"
motion.
1.2 Describe how specialised cells are adapted to their function, including:
A sperm cells – acrosome, haploid nucleus, mitochondria and tail
B egg cells – nutrients in the cytoplasm, haploid nucleus and changes in the cell membrane after
fertilisation
C ciliated epithelial cells
Specialisation in SPERM CELLS:
> Acrosome: This is the top of the head, it contains digestive enzymes which break down the outer layers of
membrane of the egg cell
> Haploid nucleus: The nucleus is found in the head. Its nucleus only has 23 chromosomes, instead of the
normal 46, so it has half the number of chromosomes, so it can combine with the egg cell (which also has 23
chromosomes) to form a 43-chromosome cell.
> Mitochondria: This is the site of respiration which supplies energy for the cell to move. Sperm cells have a
middle section that is filled with mitochondria to provide the energy needed for them to swim the long distance to
the egg cell.
> Tail: Sperm cells have a streamlined head and tail to help them swim.
Specialisation in EGG CELLS:
> Nutrients in the cytoplasm: This is so that the zygote (when a sperm and egg cell have combined, it forms a
zygote) can grow.
> Haploid nucleus: Its nucleus only has 23 chromosomes, instead of the normal 46, so it has half the number of
chromosomes, so it can combine with the sperm cell (which also has 23 chromosomes) to form a
43-chromosome cell.
> Changes in the cell membrane after fertilisation: The egg cell is surrounded by a special membrane which
becomes impermeable following fertilisation to not allow any more sperm inside.
Specialisation in CILIATED EPITHELIAL CELLS:
> Cilia: These are long, hair-like structures that move in unison to waft bacteria trapped by mucus (which is
produced by nearby goblet cells) down to the stomach, where they are killed by the stomach acid. This is one of
the ways the body protects against illnesses.
Mitochondria: This is the site of respiration which supplies energy for the cell to move and ‘waft’.
1.3 Explain how changes in microscope technology, including electron microscopy, have enabled us to
see cell structures and organelles with more clarity and detail than in the past and increased our
understanding of the role of sub-cellular structures:
The two variables (two aspects that if changed, will affect the result of the image) of microscopy:
,Resolving power: The ability to distinguish between two points. The lower the RP, the more detail is seen.
Magnification: How many times larger an image is compared to the real object.
There are two types of microscopes:
> Light microscopes:
These pass light through a specimen and create a magnified image using lenses. The first light microscope was
th
made using two lenses in the late 16 century. These have two lenses, where light is illuminated from
underneath. They allowed bacteria to be seen for the first time, aswell as discovering some larger sub-cellular
objects like the nucleus. However, lots of smaller sub-ceulluar structures still couldn’t be told apart. They have a
max magnification of 2000x and a resolving power of 200nm. They are used to view LIVING tissues, cells and
large sub-cellular structures.
> Electron microscopes:
In the 1930s, the electron microscope was developed, enabling scientists to view deep inside sub-cellular
structures such as mitochondria, ribosomes, chloroplasts and plasmids.
Electrons, instead of light in light microscopes, are used to form an image because electrons have a much
smaller wavelength than that of light waves. They have a magnification of up to 2,000,000 x. They can only be
used to view NON-LIVING specimens as electron microscopes are placed in vacuum conditions.
There are further two types of electron microscopes:
- Scanning Electron Microscope: These create 3D images (at a slightly lower magnification). RP: 10nm
- Transmission electron microscope: These create 2D images detailing organelles. RP: 2nm
Magnification calculations:
Magnification of microscope = eyepiece lens x objective lens
Math skills:
1.4 Demonstrate an understanding of number, size and scale, including the use of estimations and
explain when they should be used
1.5 Demonstrate an understanding of the relationship between quantitative units in relation to cells,
including:
a milli (10^−3)
b micro (10^−6)
c nano (10^−9)
d pico (10^−12)
e calculations with numbers written in standard form
How to write in standard form:
https://www.youtube.com/watch?v=88ki39g5oRI&t=12s
1.6 Core Practical: Investigate biological specimens using microscopes, including magnification
calculations and labelled scientific drawings from observations
Aims:
To use a light microscope to examine animal and/or plant cells.
, To make observations and draw scale diagrams of cells.
Parts of the microscope that will be used:
● The eyepiece lens
● The objective lenses
● The stage - microscope slide is placed here
● The light source
● The coarse focus - used to focus the low and medium power objective lenses
● The fine focus - used to focus the high-power objective lens
● Turret - Rotates to bring the objective lenses into place
Other apparatus used:
● Forceps
● Scissors
● Scalpel
● Coverslip
● Slides
● Pipette
To carry out the experiment, the specimen must be first prepared on the microscope to be observed under a light
microscope:
> Add a few drops/place some cells, depending if liquid or solid, to the microscope slide using a pipette or a
scalpel and cover the specimen with a coverslip and gently press down to remove any air bubbles. Gloves should
be worn to ensure there is no cross-contamination of foreign cells.
> Sometimes, stains may be required to make the structures of the specimen more visible depending on the type
of specimen being examined ie tissue. Common stains are methylene blue to stain cheek cells and iodine to stain
onion cells. Some tissue samples may need to be treated with chemicals to make the tissue more rigid.
> Preventing the dehydration of tissue:
The thin layers of material placed on slides can dry up rapidly
Adding a drop of water to the specimen (beneath the coverslip) can prevent the cells from being damaged by
dehydration
> After preparing the slide:
1. Place the slide on the stage and look through the eyepiece lens
2. Turn the focus wheel to obtain a clear image
3. Start with the lowest objective lens magnification
4. Increase the magnification of the objective lens and refocus
> If images are still blurry:
● Switch to the lower power objective lens and try using the coarse focus to get a clearer image.
● Consider whether the specimen sample is thin enough for light to pass through to see the structures
clearly.
● There could be cross-contamination with foreign cells or bodies.
