1. Cell Structure & Microscopy
Prokaryotes vs. Eukaryotes
Prokaryotes (Bacteria): These are significantly smaller than eukaryotic cells. Their genetic
material is not enclosed in a nucleus. It consists of a single DNA loop, and they may also contain
one or more small rings of DNA called plasmids. They lack mitochondria and chloroplasts.
Eukaryotes (Animal & Plant): These cells contain their genetic material (DNA) enclosed within a
nucleus. They feature specialized membrane-bound organelles like mitochondria and (in plants)
chloroplasts.
Sub-cellular Structures (Mark-Scheme Vocabulary)
Nucleus: Contains chromosomes made of DNA molecules; controls cell activities.
Mitochondria: Site of aerobic respiration. You must state that this "releases energy" for the cell.
Ribosomes: The site of protein synthesis.
Chloroplasts: Found in green parts of plants; contain chlorophyll to absorb light for
photosynthesis.
Cell Wall: Made of cellulose in plants and algae, which strengthens the cell and provides
structural support.
Microscopy Calculations
Formula: Magnification = \frac{\text{Image Size}}{\text{Actual Size}}
Key Distinction: Electron microscopes have a much higher magnification and resolution than
light microscopes. This allows biologists to study cells in much finer detail, seeing internal
structures like ribosomes.
Unit Conversion: Always convert mm to \mu m by multiplying by 1000 before calculating.
2. [Triple Only] Culturing Microorganisms
Aseptic Technique (The "How" and "Why")
To grow pure cultures and prevent the growth of unwanted pathogens:
Sterilization: Petri dishes and culture media must be sterilized before use to kill existing bacteria.
Inoculation: The inoculating loop must be sterilized by passing it through a Bunsen burner flame.
Incubation: In schools, cultures should be incubated at a maximum of 25°C. This prevents the
growth of harmful pathogens that thrive at human body temperature (37°C).
Sealing: The lid of the Petri dish should be secured with adhesive tape to prevent
Prokaryotes vs. Eukaryotes
Prokaryotes (Bacteria): These are significantly smaller than eukaryotic cells. Their genetic
material is not enclosed in a nucleus. It consists of a single DNA loop, and they may also contain
one or more small rings of DNA called plasmids. They lack mitochondria and chloroplasts.
Eukaryotes (Animal & Plant): These cells contain their genetic material (DNA) enclosed within a
nucleus. They feature specialized membrane-bound organelles like mitochondria and (in plants)
chloroplasts.
Sub-cellular Structures (Mark-Scheme Vocabulary)
Nucleus: Contains chromosomes made of DNA molecules; controls cell activities.
Mitochondria: Site of aerobic respiration. You must state that this "releases energy" for the cell.
Ribosomes: The site of protein synthesis.
Chloroplasts: Found in green parts of plants; contain chlorophyll to absorb light for
photosynthesis.
Cell Wall: Made of cellulose in plants and algae, which strengthens the cell and provides
structural support.
Microscopy Calculations
Formula: Magnification = \frac{\text{Image Size}}{\text{Actual Size}}
Key Distinction: Electron microscopes have a much higher magnification and resolution than
light microscopes. This allows biologists to study cells in much finer detail, seeing internal
structures like ribosomes.
Unit Conversion: Always convert mm to \mu m by multiplying by 1000 before calculating.
2. [Triple Only] Culturing Microorganisms
Aseptic Technique (The "How" and "Why")
To grow pure cultures and prevent the growth of unwanted pathogens:
Sterilization: Petri dishes and culture media must be sterilized before use to kill existing bacteria.
Inoculation: The inoculating loop must be sterilized by passing it through a Bunsen burner flame.
Incubation: In schools, cultures should be incubated at a maximum of 25°C. This prevents the
growth of harmful pathogens that thrive at human body temperature (37°C).
Sealing: The lid of the Petri dish should be secured with adhesive tape to prevent
