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cellulose gives shape to the cell and resist entry of excess
water
suberin and lignin decrease the permeability of cell walls
cellulose is a polymer of B-glucose (unbranched/straight)
only 1,4-glycosidic bonds between monomers of B-glucose in
a cellulose molecule
every other B-glucose monomer is inverted in a cellulose
molecule
cellulose is insoluble, strong, tough, flexible and slightly elastic
cellulase digests cellulose (symbiotic bacteria secrete cellulase and so the host can
benefit)
cellulose microfibrils: contains beta glucose joined by condensation reaction forming
1,4-glycosidic bonds between beta glucose monomers
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Microfibrils are
composed of many cellulose molecules held together by hydrogen bonds
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Pectin is a polymer of galactose, pectin chains are bound together by calcium ions in the
middle lamella which glues adjacent cells to each other
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Middle lamella: is the first layer (it is made when the plant cell divides- cell plate), which
is made of pectin (a polysaccharide that holds the cell wall of adjacent cells together like
glue, it has –vely charged carboxyl group, which combines with +ve calcium ions to
make calcium pectate, which binds/holds the cellulose microfibrils on both sides in a
matrix (like glue)
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Primary cell wall is a thin single layer
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Secondary cell wall contains many thick layers;
providing strength
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Lignin is not a carbohydrate
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It is hydrophobic
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Function of plasmodesmata: communication between adjacent cells; transporting
molecules through symplast such as water and glucose
Plasmodesmata: pores in the cell wall between adjacent cells which have cytoplasm
running through it
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Tonoplast is the membrane surrounding the permanent vacuole which is filled with cell
sap
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Maintains turgidity
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Chloroplasts and amyloplasts are examples of plastids
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Amyloplast stores starch grains while chloroplasts perform photosynthesis
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Chloroplasts are double membraned organelles
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Pleural: (grana)
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The cytoplasm of chloroplasts are called stroma
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Stem is surrounded by single layer of cells called epidermis which protects cells beneath
it against invasion by pathogens
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Dead tissue
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Phloem distributes sucrose and amino acids to growing parts in the whole plant
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Movement UP and DOWN the plant
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It
is considered as packing tissue
Collenchyma have thick, uneven primary cell wall (thicker at the corners) which gives
strength
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Also it provides flexibility
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Sclerenchyma provides structural support only
Sclerenchyma cells are elongated with pointy ends
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for strength
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Waterproof
and strong
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Have pits in their walls
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hollow
Cambium: unspecialized cells that can develop into xylem or phloem, located between
phloem and xylem (stem cells)
Xylem: dead cells, all cell components are gone
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Walls are
lignified
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Lignin is
distributed in a helical way in the cell walls of xylem
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Movement up and down the plant
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Cells joined end to end, to make long tubes, the walls between
cells become perforated creating sieve plates, where the phloem sap flows through
holes in it
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• Magnesium ions are needed for the synthesis of chlorophyll, so lack of magnesium ions
result in yellowing of leaves
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• Preclinical tests are used to check for the toxicity and for the metabolism of the new
drug
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• Phase 2: drug is tested on a small number of patients affected by the disease in concern
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Phase 2: includes 2 groups, the first group is given a placebo (inactive substance) and
the second group is given the new drug this allows researchers to see if the drug works
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• Double blind trials are done to test the effectiveness of the new drug and to compare it
with an older drug
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• Phase 3: the drug is tested on a large number of patients
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The patients are randomly chosen and split into 2 groups (one
receives the new treatment and the other has an existing treatment - control: to see if
the new drug is better than current treatments)
• What is a species?
A group of closely related organisms that are capable of breeding and producing a fertile
offspring allowing gene flow between individuals
• Domain-kingdom-phylum-class-order-family-genus-species
• Species richness: measures the variety of species
• Genetic diversity: number of different alleles in a gene pool
• Relative species abundance: the number of individuals a specific species relative to the
number of all the organisms living in a community
• To measure biodiversity within a habitat: use species richness and relative species
abundance
• To measure biodiversity within a species: use genetic diversity by calculating the
heterozygosity index
• Gene pool: all the possible alleles of a gene in a population of a single species
• Allele frequency: proportion of one allele in a gene pool
• Heterozygosity index: is a measure of genetic diversity in a species
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Mechanisms of reproductive isolation: geographical, seasonal, behavioral, ecological
and mechanical
Types of speciation: hybridization, allopatric, sympatric
Geographical and ecological isolation are examples of allopatric speciation, while
mechanical, seasonal and behavioral isolation are examples of sympatric speciation
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Compound light microscope transmits light
Transmission electron microscope (TEM) transmits electron beam
Scanning electron microscope (SEM) reflects electron beam
Total magnification = magnification of objective lens x magnification of eyepiece lens
Specimens are stained before seeing them under the light microscope; this is because
different structures absorb more stain and so absorb more light creating contrast
Different types of stains bind to different cell structures
Acetic orcein stains DNA dark red
Gentian blue stains bacterial cell wall blue
Methylene blue
Hematoxylin
Acetocarmine
Advantages and disadvantages of using light microscope:
Light and easy to handle, relatively cheap, living tissue can be observed
Low resolution and magnification, staining is needed which could result in artefacts
• There must be a vacuum inside an electron microscope as the electrons are scattered
by air molecules, therefore the specimen cant be a living organism
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Heavy metals
(lead/uranium salts) absorb electrons, this is not to identify tissues but to improve
scattering of electrons
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• Scanning electron microscopes (SEM) fine beam of electron onto a specimen and
collect the electrons scattered by the surface
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Also, they produce spindle fibers involved in mitosis
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• Ribosomes are made of 2 subunits (large and small), they are made from ribosomal
RNA produced by the nucleolus and proteins
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• Endoplasmic reticulum have a single membrane(cisternae)
• Smooth endoplasmic reticulum has no ribosomes, it makes fats and lipids
• Translation takes place in the ribosomes on the rough endoplasmic reticulum, then
proteins produced fold into their tertiary structure and move into the lumen of RER
to package the protein into vesicles and transporting it to the Golgi apparatus
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• Lysosomes contain a mixture of hydrolytic enzymes surrounded by a single
membrane (involved in phagocytosis)
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• Peptidoglycan cell wall of bacteria: A large net-like molecule made up of many
parallel polysaccharide chains with short peptide cross linkages
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Crystal violet stains all cell walls purple
Iodine combines with crystal violet to form a large insoluble purple complex
Alcohol solubilizes gram negative outer membrane flushing the complex
Safranin stains all cell walls pink, gram negative cell walls becomes pink
• Bacteria shapes: cocci, bacilli, spirilla, vibrio
• Tissue: group of similar cells that have the same structure that perform a specific
function
• Crossing over between homologous chromosomes in prophase 1 takes place forming
chiasma in which sections of chromatids are broken off and exchanges with the non
sister chromatid on the other homologous chromosomes
• Independent assortment takes place in metaphase 1 in meiosis, homologous
chromosomes line up in different combinations
• Pollen grains have exine coat
• Synergids, polar nuclei, egg cell nucleus, pollen tube nucleus and generative nucleus
• Amino acids are absorbed into the cytoplasm of the pollen and used to synthesize
enzymes, directed by the pollen tube nucleus
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Enters ovary
through small hole in the embryo sac micropyle, then Generative Nucleus of pollen
grain travels down pollen tube, It divides by mitosis forming 2 male gametes Then
enters the ovule
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Diploid zygote
The other male nucleus fuses with The two polar nuclei ………
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• When acetyl groups are removed from the histones, the chromatin becomes highly
condensed and genes in the DNA can’t be transcribed because the transcription
proteins can’t bind to them — the genes are repressed
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