Edexcel A level Biology B 2024: Topic 2
Exam Questions and Answers
Cell theory - Answer>>States that new cells are formed from
existing cells and that the cell is a fundamental unit of structure,
function and organisation in all living organisms. it is considered a
unifying concept in biology
Cells, tissues and organs - Answer>>In complex organisms, cell
are organised into tissues, tissues into organs, organs into
systems
e.g.
animal↓
muscle cell → muscle → heart → circulatory system
specialised cell → tissue → organ → system
xylem vessel → xylem → vascular bundle → transport system
Plant↑
Prokaryotes - Answer>>Unicellular organisms, no membrane-
bound organelles
Bacteria - Answer>>Structure
∙70S ribosomes (50S and 30S subunits)
∙Cell surface membrane
∙Cell wall
∙Nucleoid; circular DNA in single chromosome
∙Cytoplasm
∙Plasmid(s)
[Not always present]:
∙Capsule
∙Pilli
∙Flagellem (enables some bactera to swim)
Plasmids - Answer>>A small, circular, single strand of DNA
,Often contain genes that aid the bacteria's survival e.g. antibiotic
resistance or toxin production
Can be transferred from one bacterium to another
Nucleoid - Answer>>Prokaryotes have a singular, often circular
DNA molecule. Not considered a nucleus as it is not a membrane-
bound organelle. Can take up around half of the cytoplasm
70S ribosomes - Answer>>The sites upon which proteins are
made; in prokaryotes these are 70S, smaller than the 80S found
in eukaryotes
Cell wall - Answer>>Made up of peptidoglycan; polymers of
amino acids and monosaccharides
Gram positive or gram negative
Gram positive - Answer>>Have thick walls of peptidoglycan on
the outside, which can be stained purple by crystal violet
This wall is outside the cell surface membrane
Gram negative - Answer>>Have thin walls of peptidoglycan,
with an additional outer layer of lipids and polysaccharides, which
prevent the peptidoglycan being stained purple.
Gram negative bacteria are relatively impermeable to antibiotics
such as penicillin, so being able to identify them is important
Eukaryotes - Answer>>multi-cellular organisms with membrane-
bound organelles
Organelles of animal cells and their functions - Answer>>∙
Nucleolus: region of dense DNA and protein which makes
ribosomes
, ∙Nucleus: surrounded by a double membrane (nuclear envelope)
with pores and contains the organism's DNA in the form of
chromatin; DNA molecules wound around a protein called a
histone
∙ Centrioles: two hollow cylinders arranged at right-angles to each
other, which makes a spindle fibre during cell-division
∙Lysosome: contains digestive(hydrolytic) enzymes enclosed in a
single membrane; destroys old organelles and pathogens
∙Golgi apparatus: series of single, curved sacs enclosed by a
membrane, each sac is smaller than the previous one, many
vesicles cluster around it, modifies proteins and packages them in
vesicles for transport to other parts/out of the cell
∙Mitochondria: site of aerobic respiration; main producer of ATP
∙80S ribosomes: site of protein synthesis
∙sER (smooth endoplasmic reticulum): series of single, tubular
sacs made of membrane; site of lipid synthesis
∙rER (rough endoplasmic reticulum): series of single, flattened
sacs enclosed by a membrane with 80S ribosomes on the
surface; proteins are made by the ribosomes and
modified/transported by the rER e.g. adding prosthetic groups
∙Cell surface membrane: to control movement of substances into
and out of cells
Organelles of plant cells and their functions - Answer>>∙Golgi
apparatus: same as animal cell
∙Cell wall: for support and protection, made of cellulose
∙Cell surface membrane
∙Mitochondria
∙Nuclear envelope
∙Nucleolus
∙rER
∙sER
∙Cytoplasm
∙Chloroplasts: photosynthesis
∙Vacuole: storing water and minerals
Exam Questions and Answers
Cell theory - Answer>>States that new cells are formed from
existing cells and that the cell is a fundamental unit of structure,
function and organisation in all living organisms. it is considered a
unifying concept in biology
Cells, tissues and organs - Answer>>In complex organisms, cell
are organised into tissues, tissues into organs, organs into
systems
e.g.
animal↓
muscle cell → muscle → heart → circulatory system
specialised cell → tissue → organ → system
xylem vessel → xylem → vascular bundle → transport system
Plant↑
Prokaryotes - Answer>>Unicellular organisms, no membrane-
bound organelles
Bacteria - Answer>>Structure
∙70S ribosomes (50S and 30S subunits)
∙Cell surface membrane
∙Cell wall
∙Nucleoid; circular DNA in single chromosome
∙Cytoplasm
∙Plasmid(s)
[Not always present]:
∙Capsule
∙Pilli
∙Flagellem (enables some bactera to swim)
Plasmids - Answer>>A small, circular, single strand of DNA
,Often contain genes that aid the bacteria's survival e.g. antibiotic
resistance or toxin production
Can be transferred from one bacterium to another
Nucleoid - Answer>>Prokaryotes have a singular, often circular
DNA molecule. Not considered a nucleus as it is not a membrane-
bound organelle. Can take up around half of the cytoplasm
70S ribosomes - Answer>>The sites upon which proteins are
made; in prokaryotes these are 70S, smaller than the 80S found
in eukaryotes
Cell wall - Answer>>Made up of peptidoglycan; polymers of
amino acids and monosaccharides
Gram positive or gram negative
Gram positive - Answer>>Have thick walls of peptidoglycan on
the outside, which can be stained purple by crystal violet
This wall is outside the cell surface membrane
Gram negative - Answer>>Have thin walls of peptidoglycan,
with an additional outer layer of lipids and polysaccharides, which
prevent the peptidoglycan being stained purple.
Gram negative bacteria are relatively impermeable to antibiotics
such as penicillin, so being able to identify them is important
Eukaryotes - Answer>>multi-cellular organisms with membrane-
bound organelles
Organelles of animal cells and their functions - Answer>>∙
Nucleolus: region of dense DNA and protein which makes
ribosomes
, ∙Nucleus: surrounded by a double membrane (nuclear envelope)
with pores and contains the organism's DNA in the form of
chromatin; DNA molecules wound around a protein called a
histone
∙ Centrioles: two hollow cylinders arranged at right-angles to each
other, which makes a spindle fibre during cell-division
∙Lysosome: contains digestive(hydrolytic) enzymes enclosed in a
single membrane; destroys old organelles and pathogens
∙Golgi apparatus: series of single, curved sacs enclosed by a
membrane, each sac is smaller than the previous one, many
vesicles cluster around it, modifies proteins and packages them in
vesicles for transport to other parts/out of the cell
∙Mitochondria: site of aerobic respiration; main producer of ATP
∙80S ribosomes: site of protein synthesis
∙sER (smooth endoplasmic reticulum): series of single, tubular
sacs made of membrane; site of lipid synthesis
∙rER (rough endoplasmic reticulum): series of single, flattened
sacs enclosed by a membrane with 80S ribosomes on the
surface; proteins are made by the ribosomes and
modified/transported by the rER e.g. adding prosthetic groups
∙Cell surface membrane: to control movement of substances into
and out of cells
Organelles of plant cells and their functions - Answer>>∙Golgi
apparatus: same as animal cell
∙Cell wall: for support and protection, made of cellulose
∙Cell surface membrane
∙Mitochondria
∙Nuclear envelope
∙Nucleolus
∙rER
∙sER
∙Cytoplasm
∙Chloroplasts: photosynthesis
∙Vacuole: storing water and minerals
