subject guide notes

A2.2.1—Cells as the basic structural unit of all living organisms

Cell theory has 3 basic principles:

  1. all living things are made of cells

  2. cells are the basic unit of life & are the smallest unit of life

  3. cells come only from other cells

before cell theory, it was believed that life could appear only from non-living matter (called the spontaneous generation theory)

  • supported by the Rotting Meat experiment (check handouts for info on that)

A2.2.2—Microscopy skills *check kognity for practice questions

note that image size is AKA as measured length, meaning u acc measure the image, and whatever u get is the image size. the actual size is whatever number is given as the measurement

A2.2.3—Developments in microscopy

Electron microscopes hv a shorter wavelength than light, meaning they hv a higher resolution than light microscopes

  • can identify small objects very well

Light microscopes are useful for studying tissues & living cells in color, cuz they don’t damage the specimen

following techniques allow scientists to study biological samples at greater resolution

Freeze fracture microscopy - good for examining structures that normally aren’t visible, such as internal plasma membrane

Cryogenic electron microscopy - improves image’s resolution & limits damage done to sample

Immunofluorescence - allows for identification of target molecules as the structure emits a light of different wavelength

Fluorescent dyes - will attach to certain structures, & these areas will appear brighter, which can be detected

  • can also be used to monitor drug delivery

A2.2.4—Structures common to cells in all living organisms

DNA is the genetic material

Cytoplasm primarily composed of water

plasma membrane composed of lipids, that encapsulates the cell contents

i think these are all common cuz they’re the basic components needed to support an independent unit of life

A2.2.5—Prokaryote cell structure

prokaryotes are also unicellular

Cell wall - protects cell against toxins, resists high osmotic pressure & maintains cell’s shape

Plasma membrane - separates cell’s interior from exterior & controls the entry & exit of substances

Cytoplasm - a water-based fluid that fills the cell

  • it suspends ions, organic molecules, DNA & ribosomes

  • is where metabolic reactions occur

DNA - DNA is naked (isn’t associated with histone proteins), & found in region called nucleoid

70S ribosomes - are where translation (protein synthesis) occurs

  • are smaller & hv a lower mass than eukaryotic ribosomes

Plasmid - small, circular pieces of DNA that can be transferred from one cell to another

many contain a capsule - an outer layer of polysaccharides that protects cell

some also hv a flagellum - moves the organism by propelling

some hv pili (singular: pilus) - protein filaments on cell wall that help in cell adhesion & in transferring DNA between 2 cells

A2.2.6—Eukaryote cell structure

eukaryotes are multicellular

large diversity within eukaryotes

  • leaf cells, motor neuron

plasma membrane - separates cell’s interior from exterior & controls entry & exit of substances

cytoplasm - a jelly-like substance inside the cell

  • contains organelles

  • is where metabolic reactions occur

80S ribosomes - bigger & hv larger mass than 70S ribosomes

  • is where protein synthesis (translation occurs)

  • hv be attached or free-floating

Mitochondria - convert glucose into ATP during respiration

Nucleus - contains DNA (that’s associated with histone proteins & sorted into chromosomes)

  • contains nucleolus (location of protein synthesis)

  • has double membrane with pores, allowing certain molecules to pass through

Organelles: hv specific functions

  • smooth endoplasmic reticulum - produces & stores lipids (ex: steroids)

  • rough endoplasmic reticulum - has ribosomes on its surface, which produce proteins that are sent outside the cell

  • golgi apparatus - processes & packages proteins

  • vesicle - transports & releases substances produced within cell by fusing with cell membrane

  • vacuole - helps maintain osmotic balance

    • may also store substances

  • cytoskeleton - is a system of microtubules & microfilaments

    • helps hold organelles in place

    • maintains structure of cell

A2.2.7—Processes of life in unicellular organisms

unicellular organisms can perform all these functions

multicellular organisms hv specialised cells to carry out some of these functions

  • but as a whole, the organism will perform all these functions

metabolism - chemical reactions that take place within the cell(s) of an organism

response to stimuli - reacting to changes in the external environment

homeostasis - the maintenance of constant internal conditions, despite changes in their external environments

movement - living things have some control over their place and position

growth - cells can increase in size over a period of time. In multicellular organisms, growth can also refer to an increase in the number of cells that make up an organism

reproduction - the production of offspring. Reproduction can be sexual or asexual

excretion - the removal of metabolic waste products

nutrition - the intake or production of nutrients. Heterotrophic organisms obtain their nutrients from the external environment, whereas autotrophic organisms are able to produce nutrients from inorganic material

A2.2.8—Differences in eukaryotic cell structure between animals, fungi and plants

presence & composition of cell walls:

animal cells - no cell wall

plant cell - hv cell wall made of cellulose

  • protects cell & helps it resist osmotic pressure, maintaining shape of cell

fungi - hv cell wall made of chitin

differences in sizes & functions of vacuoles:

animal cell - some hv vacuoles

  • are smaller

  • store water, nutrients & waste products

plant cell - hv vacuole

  • larger than in animal cells

  • important for regulating osmotic potential of cell

fungi - contain large vacuoles

  • break down molecules in cell

  • store smaller molecules (such as ions)

presence of chloroplasts & other plastids

animal cell - hv none of that

plant cell - hv both

  • chloroplast - converts light energy into chemical energy

fungi - hv none of that

presence of centrioles, cilia, and flagella

animal cell - hv first 2

  • centrioles help establish & organise microtubules, playing important role in cell division

  • some hv cilia - important for moving substances past cell

    • ex: many cilia on epithelial cells of bronchi, which move debris up & out of respiratory tract

plant cell - hv none of the 3

fungi - hv first 2

  • centrioles produce & organise cytoskeleton, playing important role in cell division

    • but aren’t present in most fungi, except for male gametes of some fungi

    • main function is to produce cilia

A2.2.9—Atypical cell structure in eukaryotes

  • means they don’t contain any organelles typically found in eukaryotic cells, or they contain an abnormal amount of organelles

skeletal muscle - is multinucleated (one cell contains multiple nuclei)

  • this is cuz the muscle cell formed from multiple smaller myocytes that fused together

RBC’s - anucleate (don’t hv nucleus)

  • allows cell to hv higher haemoglobin capacity (meaning there’s more space for haemoglobin) & oxygen

aseptate hyphae - multinucleated

  • don’t hv cellular partitions, meaning there’s multiple nuclei in a single cellular unit

sieve tube elements - anucleate

  • contain little cytoplasm & organelles

  • means there’s little resistance for substances moving through a sieve tube element

(not on subject guide but just a note)

advantages of compartmentalisation

  • ability to establish higher concentrations of certain substances within organelles

  • ability to separate toxins from rest of cell

    • ex: hydrolytic enzymes are stored in lysosomes

  • control over conditions in organelles (such as pH) in order to maintain the optimal conditions for efficient enzyme function

A2.2.10—Cell types and cell structures viewed in light and electron micrographs

NEED TO LEARN

A2.2.11—Drawing and annotation based on electron micrographs

remember to include function of organelles in drawings

A2.2.12—Origin of eukaryotic cells by endosymbiosis

evidence suggests that eukaryotic organisms evolved from a common unicellular ancestor

  • this common ancestor endocytosed a prokaryotic cell, which generated energy from oxygen

  • instead of being digested, these cells remained in the host cell, and performed aerobic respiration, providing energy to their host cell, eventually evolving into mitochondria

chloroplast likely evolved when eukaryotes endocytosed a prokaryotic cell that could convert light energy into chemical energy

evidence

both mitochondria & chloroplasts:

  • measure around 8 μm in length, the same size as many prokaryotic organisms

  • hv double membranes

  • hv circular naked DNA, as found in prokaryotes

  • hv 70S ribosomes, the same size as ribosomes in prokaryotes

  • divide by binary fission (as do prokaryotes)

  • susceptible to some antibiotics

A2.2.13—Cell differentiation as the process for developing specialized tissues in multicellular organisms

involves the turning on of certain genes that are responsible for the function of a specialised cell & the turning off of genes that aren’t needed for the function of a specialised cell

  • these differences in gene expression are typically triggered by the environment

A2.2.14—Evolution of multicellularity

multicellularity evolved repeatedly through cell aggregation

  • is when individual cells cluster together, meaning they can efficiently obtain & share nutrients

  • over time, some cells within cluster were thought to hv differentiate to play for specialised roles

multicellularity also has the advantage of hv a larger body size & being able to adapt to their environment