1.1 Introduction to cells
Cell theory
- All living organisms are composed of cells
- Cells are the basic unit of life → smallest living structure
- New cells arise from pre-existing ones
Common features of cells
- Plasma membrane → separates cell contents from outside
- Genetic material → instructions for cell activities (chemical reactions catalyzed by
enzymes)
- Energy release system → powers cell activities
𝑖𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒
Magnification= 𝑎𝑐𝑡𝑢𝑎𝑙 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 𝑠𝑖𝑧𝑒
- 1 mm = 1000 µm (micrometres)
- 1 µm = 1000 nm (nanometres)
Cells that do not conform to cell theory
- Striated muscle fibre → long, multinucleated fibres
- Challenges the idea that cells always function as autonomous units
- Aseptate fungal hyphae → no cellular partitions
- Challenges the idea that living structures are composed of discrete cells.
- Giant algae → unicellular; 100mm
- Challenges the idea that larger organisms are always made of many
microscopic cells
7 functions of life (MRGREHN)
- Metabolism
- Response
- Growth
- Reproduction
- Excretion
- Homeostasis
- Nutrition
- Movement (optional)
Surface area to volume ratio
- Rate of metabolism (chemical reactions in cytoplasm) → cell volume
- Rate at which substances cross cell membrane → surface area
- Too small → substances enter less quickly than required; waste products accumulate
(production > excretion)
- Overheat because metabolism produces heat faster than it is lost over the
cell’s surface.
Only the nucleus, cell wall, cell membrane, chloroplast and secretory vesicles can be seen
under the light microscope. (+ cytoplasm if stained)
, Paramecium Chlamydomonas
Reproduction Asexual Asexual
Sexual (nuclei fuse and
divide)
Nutrition Vacuoles digest smaller Photosynthesis
organisms Absorbing carbon
compounds
Excretion waste diffuses out through cell membrane
Homeostasis Contractile vacuoles fill up & expel water
Metabolism Enzymes in the cytoplasm Photosynthesis inside
chloroplasts in cytoplasm
Movement Beating of the cilia (changes Beating 2x flagella
in environment) (light-sensitive eyespot)
Multicellular organisms
- Emergent properties → arise from interaction of component parts of complex
structure
- Differentiation: development of cells in different ways to carry out specific functions →
carry out role more efficiently (develop ideal structure + enzymes for function
reaction)
- Many same specialized cells = tissue
- happens because a different sequence of genes is expressed in development
of different cell types
Stem cells
- Divide repeatedly to produce large quantities of new cells → grow tissue and replace
damaged cells
- Not fully differentiated → can differentiate in different ways to produce new cell types
- Stargardt’s disease → photoreceptive cells in the retina degenerate (ABCA4
prevents active transport)
- Treatment → develop embryonic stem cells into retina cells and injecting it
into the eyes.
, - Leukaemia → mutations cause uncontrolled cell division of abnormal white blood
cells → chemotherapy kills both cancer cells and white-blood cell producing stem
cells
- Treatment → adult stem cells extracted from arrow and returned post chemo
→ establish and multiply producing red and white blood cells
Embryonic stem cells Cord blood stem cells Adult stem cells
Limited quantities
Easily obtained Difficult to obtain
Almost unlimited growth Less growth potential
potential
Higher chance of malignant Less chance of malignant
tumours tumours
Can differentiate into any
type Limited capacity to differentiate
Genetically different
Fully compatible
Removal kills embryo
Removal does not kill the adult
Stem cell research is ethical Stem cell research is unethical
Potential to cure incurable diseases → Embryo = human, killing it for stem cells is
reduces suffering unethical → considered human when
fertilized/brain; heartbeat; bone tissue?
No human characteristics or pain → simply creating embryos via IVF for sole purpose
groups of cells of stem cells
IVF involves hormone treatment + invasive
surgical procedures → exploitation of
vulnerable women
, 1.2 Ultrastructure of cells
Electrons have a shorter wavelength than light (400-700nm) → Electron microscopes =
(0.001 µm/1nm); Light microscopes =0.2 µm/200nm → electron microscopes reveal the
ultrastructure
Prokaryotic cells (0.1 to 5μm)
- No nucleus → nucleoid region containing DNA (appears lighter because it is not
associated with proteins)
- Cytoplasm is not compartmentalized
- Only 70S ribosomes in cytoplasm
- Cell wall → protect cell, maintain shape & prevent bursting (contains peptidoglycan)
- Divide via binary fission (asexual reproduction = genetically identical)
- Single chromosome replicated → 2 copies move to opposite ends →
cytoplasm divides
Eukaryotic cells (10 to 100μm)
- Nucleus contains chromosomes
- Compartmentalized with single/double membranes → organelles
- Concentrates enzymes for particular process
- Damaging substances kept inside membrane of organelle
- Organelles w/ contents moved around
- Conditions (e.g. ph) can be ideal level for particular process (different level for
other processes elsewhere)
Organelles in eukaryotic cells
Nucleus
- DNA is replicated/transcribed into
mRNA → exported via nuclear
pores to cytoplasm
Rough ER
- Synthesize protein → passes into
cisterna & carried to Golgi by
vesicles
Golgi apparatus
- Processes rER proteins → carried in
vesicle to membrane for secretion
Lysosome
- Contain digestive enzymes → break
down ingested
food/organelles/whole cell
Mitochondrion
- Produce ATP via aerobic respiration
- Digests fat if used as energy source
Cell theory
- All living organisms are composed of cells
- Cells are the basic unit of life → smallest living structure
- New cells arise from pre-existing ones
Common features of cells
- Plasma membrane → separates cell contents from outside
- Genetic material → instructions for cell activities (chemical reactions catalyzed by
enzymes)
- Energy release system → powers cell activities
𝑖𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒
Magnification= 𝑎𝑐𝑡𝑢𝑎𝑙 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 𝑠𝑖𝑧𝑒
- 1 mm = 1000 µm (micrometres)
- 1 µm = 1000 nm (nanometres)
Cells that do not conform to cell theory
- Striated muscle fibre → long, multinucleated fibres
- Challenges the idea that cells always function as autonomous units
- Aseptate fungal hyphae → no cellular partitions
- Challenges the idea that living structures are composed of discrete cells.
- Giant algae → unicellular; 100mm
- Challenges the idea that larger organisms are always made of many
microscopic cells
7 functions of life (MRGREHN)
- Metabolism
- Response
- Growth
- Reproduction
- Excretion
- Homeostasis
- Nutrition
- Movement (optional)
Surface area to volume ratio
- Rate of metabolism (chemical reactions in cytoplasm) → cell volume
- Rate at which substances cross cell membrane → surface area
- Too small → substances enter less quickly than required; waste products accumulate
(production > excretion)
- Overheat because metabolism produces heat faster than it is lost over the
cell’s surface.
Only the nucleus, cell wall, cell membrane, chloroplast and secretory vesicles can be seen
under the light microscope. (+ cytoplasm if stained)
, Paramecium Chlamydomonas
Reproduction Asexual Asexual
Sexual (nuclei fuse and
divide)
Nutrition Vacuoles digest smaller Photosynthesis
organisms Absorbing carbon
compounds
Excretion waste diffuses out through cell membrane
Homeostasis Contractile vacuoles fill up & expel water
Metabolism Enzymes in the cytoplasm Photosynthesis inside
chloroplasts in cytoplasm
Movement Beating of the cilia (changes Beating 2x flagella
in environment) (light-sensitive eyespot)
Multicellular organisms
- Emergent properties → arise from interaction of component parts of complex
structure
- Differentiation: development of cells in different ways to carry out specific functions →
carry out role more efficiently (develop ideal structure + enzymes for function
reaction)
- Many same specialized cells = tissue
- happens because a different sequence of genes is expressed in development
of different cell types
Stem cells
- Divide repeatedly to produce large quantities of new cells → grow tissue and replace
damaged cells
- Not fully differentiated → can differentiate in different ways to produce new cell types
- Stargardt’s disease → photoreceptive cells in the retina degenerate (ABCA4
prevents active transport)
- Treatment → develop embryonic stem cells into retina cells and injecting it
into the eyes.
, - Leukaemia → mutations cause uncontrolled cell division of abnormal white blood
cells → chemotherapy kills both cancer cells and white-blood cell producing stem
cells
- Treatment → adult stem cells extracted from arrow and returned post chemo
→ establish and multiply producing red and white blood cells
Embryonic stem cells Cord blood stem cells Adult stem cells
Limited quantities
Easily obtained Difficult to obtain
Almost unlimited growth Less growth potential
potential
Higher chance of malignant Less chance of malignant
tumours tumours
Can differentiate into any
type Limited capacity to differentiate
Genetically different
Fully compatible
Removal kills embryo
Removal does not kill the adult
Stem cell research is ethical Stem cell research is unethical
Potential to cure incurable diseases → Embryo = human, killing it for stem cells is
reduces suffering unethical → considered human when
fertilized/brain; heartbeat; bone tissue?
No human characteristics or pain → simply creating embryos via IVF for sole purpose
groups of cells of stem cells
IVF involves hormone treatment + invasive
surgical procedures → exploitation of
vulnerable women
, 1.2 Ultrastructure of cells
Electrons have a shorter wavelength than light (400-700nm) → Electron microscopes =
(0.001 µm/1nm); Light microscopes =0.2 µm/200nm → electron microscopes reveal the
ultrastructure
Prokaryotic cells (0.1 to 5μm)
- No nucleus → nucleoid region containing DNA (appears lighter because it is not
associated with proteins)
- Cytoplasm is not compartmentalized
- Only 70S ribosomes in cytoplasm
- Cell wall → protect cell, maintain shape & prevent bursting (contains peptidoglycan)
- Divide via binary fission (asexual reproduction = genetically identical)
- Single chromosome replicated → 2 copies move to opposite ends →
cytoplasm divides
Eukaryotic cells (10 to 100μm)
- Nucleus contains chromosomes
- Compartmentalized with single/double membranes → organelles
- Concentrates enzymes for particular process
- Damaging substances kept inside membrane of organelle
- Organelles w/ contents moved around
- Conditions (e.g. ph) can be ideal level for particular process (different level for
other processes elsewhere)
Organelles in eukaryotic cells
Nucleus
- DNA is replicated/transcribed into
mRNA → exported via nuclear
pores to cytoplasm
Rough ER
- Synthesize protein → passes into
cisterna & carried to Golgi by
vesicles
Golgi apparatus
- Processes rER proteins → carried in
vesicle to membrane for secretion
Lysosome
- Contain digestive enzymes → break
down ingested
food/organelles/whole cell
Mitochondrion
- Produce ATP via aerobic respiration
- Digests fat if used as energy source
