A cheat sheet for the whole of B1 (Cell Level Systems) Biology, providing detail to get top grades. Designed for OCR Gateway A Triple science, however can be used for any biology revision. Includes: microscopes, subcellular structures, dna, respiration, protein synthesis, food tests, and photosynth...
Biology - B1 (Cell level Syste
Microscopes:
Microscopes magnify the image of a specimen - cells, tissues or other structures - s
appears larger.
How to prepare a microscope slide:
A specimen is placed onto a slide, where it is sometimes stained in order to see the
specimen clearly. Then a cover slip is placed onto the specimen to cover it, and is a
placed at an angle in order to not form any air bubbles underneath the coverslip an
affect what we see in the microscope. Then the slide is placed onto the stage where
clipped on using the stage clips and you look through the eyepiece. You always sta
the smallest objective lens first and increase the magnification until you can see cle
Definitions:
Magnification: The degree to which the size of an image is
larger than the real object.
Magnification of an object = image size/ object size
Magnification of the microscope: magnification of the eyepiece
lens x the magnification of the objective lens
Labelled diagram of a Light Microscope
Resolution: the ability to distinguish between 2 points which
are close to each other.
Advantages Disadvantages Electron microscope uses electrons rather than light in order to produce an image.
Because of the small wavelength electrons have in comparison to visible light, this
~Cheaper ~Low resolution allows them to see subcellular structures. There are 2 types:
~Doesn’t require ~Low magnification SEM: Scanning electron microscopes which produces 3D images but has a lower
specialist training strength resolution
~Can look at living ~Some organelles TEM: Transmission electron microscopes which produces a 2D image but at a high
specimen require staining to be resolution
viewed
Structures and their functions:
Advantages and disadvantages of a light microscope
Nucleus: Contains the genetic material and controls cell
activity
Advantages Disadvantages Cytoplasm: Site of all chemical reactions within the cell
Ribosomes: Site of protein synthesis
~Can see very small ~Expensive Mitochondria: Site of aerobic respiration
organelles ~Requires specialist Cell membrane: Controls what enters and leaves
~Can produce a 3D training Cell wall: Supports the cell shape and made of cellulose
image (SEM) ~Can only view dead Vacuole: Contains cell sap
specimen Chloroplast: Where photosynthesis takes place
~Cannot be moved Cell wall (prokaryotic): made of peptidoglycan
Plasmid: Small rings of DNA
Advantages and disadvantages of an electron microscope
DNA: Respiration:
DNA (deoxyribonucleic acid) is a Aerobic respiration: Uses oxygen and gets th
polymer in the shape of a double ATP (cell energy) to the cells and the reactio
helix. A section of DNA codes for a place in the mitochondria.
gene, and DNA winds up tightly to C6H12O6 + O2 → CO2 +H2O
make a chromosome. The bases in Glucose + oxygen → carbon dioxide + water
DNA join together in complementary
base pairings, A - T and C - G. Anaerobic respiration: Doesn’t require oxyge
gets less ATP to cells in comparison to aerob
respiration. It’s a last resort, as it produces a
product called lactic acid.
Protein Synthesis:
In animals:
There are only 2 steps in protein synthesis: C6H12O6 → 2C3H6O3
transcription and translation. Glucose → Lactic acid
Transcription takes place within the cell and is
when the DNA is unzipped and a mRNA nucleotide In plants and yeast (fermentation for bread a
(messenger RNA) and a copy of the DNA is made alcohol):
in the nucleus before exiting through the porous C6H12O6 → C2H5OH + CO2
membrane. Glucose → Ethanol + Carbon dioxide
Translation happens outside the nucleus and its
when the mRNA goes to the ribosome, and the
ribosome connects the tRNA nucleotide (transfer
RNA) and the mRNA to create the full DNA chain
and then the corresponding amino acids fold into a
protein.
DNA codes in triplets so every 3 bases code for a
different amino acid.
In the mRNA, the base “T” is replaced with the Enzymes:
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