Some organisms are composed of only one cell (paramecium, chlamydomonas, euglena, chlorella, amoeba, etc.)
This single cell has to carry out all the activities essential to living organisms

Prokaryotic cell structure

Eukaryotic cell structure

Animal

Plant

Multicellular organisms

Organisms that consist of many cells
These cells do not have to carry out many different functions
Instead they can become specialized for one particular function and carry it out very efficiently. This is called differentiation (muscle cell, nerve cell, xylem cell)
Each cell has all the genes for the organism but only certain genes are turned on, the ones needed for that particular cell function. The others are switched off because the cell does not carry out that function (gene expression)

Emergent properties

Interaction between different cells to create new functions
Allows multicellular organisms to complete functions that individual cells cannot (cell → tissue → organ → system)

Membrane structure

Phospholipid bilayer
Phosphate heads = hydrophilic, fatty acid tails = hydrophobic, amphipathic
Fluid mosaic model (cholesterol allows movement, proteins=integral or peripheral)

Membrane models

Davson-Danielli: two outer layers of protein flank an inner phospholipid bilayer

Problems with this model were:

Assumed all membranes were of uniform thickness
Assumed all membranes have symmetrical internal and external purposes
Did not account for permeability of certain substances
Temperatures at which membranes solidified did not correlate with those expected under proposed model
Singer-Nicolson: proteins imbedded within phospholipid bilayer instead of existing as separate layers

Functions of membrane proteins = JETRAT

Junction: to connect and join two cells together
Enzymes: fixing to membrane localises metabolic pathways
Transport: responsible for facilitated diffusion and active transport
Recognition: may function as markers cellular identification
Anchorage: attachment points for cytoskeleton and extracellular matrix
Transduction: function as receptors for peptide bonds

Glycoprotein: carbohydrate group attached to a protein

Glycolipid: made of carbohydrates and lipids, function is to act as a receptor/helps cells recognise specific molecules

Stem cells

Self renewal: can divide and replicate
Potency: capable

Examples of therapeutic uses

Stargardt’s disease (replacing dead retinal cells to treat macula dystrophy)
Grafting new skin cells in burns victims
Replacing nerve cells in spinal injuries
Bone marrow transplants for patients on chemotherapy

Ethics of Stem cells

Embryonic cells

Have almost unlimited growth potential
Can be generated artificially by SCNT
Involves the destruction of an embryo
Higher risk of cancer development

Umbilical cord blood of newborn

Easy to extract from umbilical cord
Cells must be stored from birth at cost

Adult tissues (e.g bone marrow)

Can be obtained at any stage of life
Cells may be difficult
Lowest growth potential (multipotent)

Movement across the membrane

Diffusion:

Passive transport
Movement of substances along the concentration gradient from an area of high to low concentration
Oxygen, carbon dioxide
No energy required
Phospholipid bilayer

Facilitated diffusion:

Proteins in the membrane help large/polar molecules pass through
Glucose, polar molecules (H+, Na+)
No energy required
Phospholipid bilayer, proteins (channel and carrier proteins)

Active transport

Uses energy to allow the movement of molecules against the concentration gradient from low to high concentration
Glucose, Na+, K+
ATP required
Carrier proteins, phospholipid bilayer

Endocytosis

The taking in of substances (from low to high concentration, type of active transport)
Solids, liquids, gases
Energy required
Vesicles, phospholipid bilayer

Exocytosis

Opposite of endocytosis
Waste products, cellulose
Energy required
Vesicles, phospholipid bilayer

Osmosis

Osmosis is the passive movement of water molecules from an area of high solvent (low solute) concentration to low solvent (high solute) concentration

Solute concentration is what affects the movement of water
Diffusion of water
Passive process (no energy required)
Membrane is essential

Osmolarity → total concentration of active solutes in the solution

High osmolarity = high concentration of solutes

Hypertonic solution → plasmolyzed

High osmolarity than the tissue
More solutes
Water moves out of the tissue

Hypotonic solution → turgid

Has lower osmolarity than the tissue
Less solutes
Water moves into the tissue

Isotonic → flaccid

Equal osmolarity
No net movement of water

In bold = for plant cells ONLY

For animal cells:

Plasmolyzed → crenate

Turgid → lysis

Final mass (or length) - starting mass (or length)

—-------------------------------------------------------------

Starting mass (or length)

Origins of cells

Spontaneous generation (living thing spawns from non-living thing)
Francisco Reidi → saw maggots develop on raw meat exposes to air
Louis Pasteur poured meat broth into two flasks with S shaped necks and boiled them to ensure all life was eliminated. No life formed after 3 years. Shook one of the flasks and the microorgnasims on the dust that had formed well into the solution and caused colour change. Argued that organisms had always existed in the dust and did not spontaneously generate
Arrenhius → panspermia (seeds everywhere), space is teeming with tiny life forms, travel through the cosmos in space objects, some of the seeds make it the Earth
Carbon is the essence of life, carbon is in stars, we are made of stardust
Miller and Ureys → Recreated early atmosphere using hydrogen, methane and ammonia, boiling water represents the sea, sparks represent electrical storms,
process: water boils, steam rises, coils and condenses, steam mixes with gases and falls back into the sea, cycle repeats
A red sludge formed at the bottom, amino acids (building blocks of proteins)
Crick and Watson → discovered the structure of DNA, idea of having a genetic code, sequence of rungs along DNA strand determines how amino acids are ordered to build our bodies, order gives instructions for certain protein formations
For DNA instructions to be converted into amino acid sequences, RNA is required
Before DNA world, RNA world
Altman and Cech → RNA molecules that could “snap” out parts of other RNA molecules, not just relaying messages
Ribose forms the backbone of RNA, made up of elements from the primordial soup (compounds come from outer space)
Mixing of stardust in the deep ocean may have formulated RNA
Endosymbiosis: one organism lives inside of another organism, both organisms benefit from it, DNA absorbed, transferred to offspring
Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis

Cell division

During growth
Tissue repair
Asexual reproduction
G1-2 (increase cytoplasm volume, organelles produced, protein synthesis)
S (DNA replication)
Centromere, sister chromatids, centrioles/centrosome, spindle fibers
Prophase (chromosomes supercoil, nucleus)
Metaphase (Chromosomes line up at equator of the cell)
Anaphase (sister chromatids pulled to opposite sides by spindle fibers)
Telophase (cleavage furrow forms, nucleus forms)
Cytokinesis (in plant cells, membrane bound vesicles fuse to form double membranewhich enclose cell plate at equator of the cell, materials secreted into space between membranes to form new cell wall) (in animal cells, ring of microfilaments develop around cell, attach to plasma membrane, cleavage furrow)

Mutation

Change in organisms genetic code
Mutagens → agents that cause gene mutations (short wave UV lights, some viruses)
Carcinogens → chemicals that cause mutations
Mutations in oncogene → malfunction in control of cell cycle → uncontrolled cell division → tumour formation
Several mutations must occur for tumour, very rare
Factors that can increase chance of tumour formation: the greater the number of cells the greater the possibility, the longer the life span the greater the possibility

Cancer

Benign (growth remains at the original site)
Malignant (spreads around body to form secondary tumors, this splitting off of cancerous cells is called metastasis, cancerous cells are often carried in the blood, this form is more serious and harder to treat)

Forms of cancer treatment:

Surgery (surgically remove all of the cancerous cells)
Chemotherapy (chemicals used to try to interfere with the uncontrolled cell division, mitotic index can be used to predict the response of cancer cells to chemotherapy)
Radiotherapy (use of radiation to kill cancerous cells)

Causes: asbestos, cigarette smoke, electromagnetic radiation (UV, X-rays)

Mitotic index

Number of actively dividing cells in view

—-------------------------------------------------

Number of total cells in view

Cyclins