AS Level Biology Chapters 1 and 2

What is a prokaryote?

A cell that has no nucleus - ‘‘pro’’ (before) nucleus

What is an eukaryote?

A cell that has a nucleus - ‘‘eu’’ (true) nucleus

What is an unicellular organism?

An organism that is made of one cell

What is a multicellular organism?

An organism made of many/multiple cells

What is the thickness of the cell surface membrane?

7nm (5-10nm)

To get um from cm, what do you need to do

Multiply the cm value by 10^4

To get mm from nm, what do you need to do?

Multiply the nm value by 10^-6

What is the formula for image size, actual size, and magnification?

I/AM

Define magnification

Enlargement of a specimen

Define resolution

The minimum distance two objects can be, in order to be viewed as seperate items. I.e how close two objects can be together and still be viewed seperately.

What is the maximum resolution of a light microscope?

200nm wavelength- therefore objects closer than 200nm to one another will be seen as one object. Objects smaller than 200nm won’t be seen

What is wavelength?

The space between waves (of light e.g)

Resolution of an electron microscope?

0.1nm to 30nm wavelength

What is an artefact?

Features that appear in a micrograph due to the handling of the specimen (e.g tears or cuts)

What type of image does a scanning electron micrograph show?

3d, only the contours of the cell(s)/topography, gives larger area of depth that is sharp

What type of image does a transmission electron micrograph show?

2d, internal cell features visible, represents one plane of view so many planes are required to construct a picture

In what state must specimens being observed with an electron microscope be in?

They must be dead

What is the maximum magnification of a light microscope?

1500x

What surrounds animal and plant cells?

An extracellular matrix

What organelles are in plant cells only? (in comparison to animal cells)

(Cellulose) cell wall, vacuole, chloroplasts, plasmodesmata, starch grains and granules

What organelles are in animal cells only? (in comparison to plant cells)

80s ribosomes, cilia, centrioles, microvilli, glycogen granules

Are centrioles required for mitosis?

In animal cells yes, in plant cells no; the spindle forms and the sister chromatids are seperated.

What is the average diameter of a nucleus?

10-20um

What are the four parts of a nucleus?

1. The nuclear envelope

2. Pores within the nuclear envelope to allow large molcules like mRNA and RNA (ribosomes) to exit

3. Non-condensed DNA complexed with histone proteins (chromatin)

4. Nucleolus - where rRNA and ribosomes are manufactured and assembled

If protein synthesis was to be stopped, from where would it initiate?

The nucleus. No more mRNA produced would mean no more polypeptides.

What is the function of chloroplasts?

Photosynthesis

Chloroplast diameter and thickness?

Diamter = 3um-10um, thickness = 1um

What are the four components of the chloroplast?

1. Chloroplast envelope - double membrane - to control the entry and exit of substances

2. Grana - stack of thylakoids (looks like coins)

3. Stroma - jelly like matrix. Contains oil droplets, small circular DNA and 70s ribosomes

4. Starch grains - Temporary store of the carbohydrates produced during photosynthesis

Mitochondria shape, length and diameter?

Rod shaped, 1-7um, 0.5-0.1um

What are the three components of mitochondrion?

1. Double membrane that controls entry and exit of substances

2. Cristae - infoldings of the inner membrane

3. Matrix containing small circular DNA molecules, mitochondrial DNA and 70s ribosomes

What is the name of the appearance of flattened sacs of endoplasmic reticulum?

Cisternae

What does rough endoplasmic reticulum (RER) have that smooth endoplasmic reticulum (SER) doesn’t?

80s ribosomes on the outer surfaces of the membranes

What does the RER do?

It modifies proteins in its lumen, provides a pathway for proteins throughout the cell and forms transport vesicles which go the the golgi body for further processing. Because it has so many ribosomes on its outer surface membrane, a lot of polypeptide synthesis occurs near the RER lumen.

What does the SER do?

Synthesises lipids like cholesterol in the SER lumen and stores and transports them. Like the RER, it also forms vesicles to transport these lipids to the golgi body.

What do both SER and RER have?

Both have a lumen where they process their respective molecules

What does the Golgi body do?

Modifies and processes proteins and lipids and then packages them into golgi vesicles, they form primary lysosomes.

Give three examples of protein modification that can occur either in the RER or Golgi body:

Adding non-protein components, folding of proteins into their final shape, joining of polypeptides to make a functioning protein

What is the name for the convex side of the Golgi body?

Cis face, where transport vesicles arrive. Faces the nucleus.

What is the name of the concave side of the Golgi body?

Trans face, where golgi vesicles are produced. Faces the cell surface membrane.

How many membranes do lysosomes have?

One, they are single membrane bound organelles

What is the function of a lysosome?

Digest old cells, bacteria, dead cells and the release of hydrolytic enzymes out of the cell

How big are lysosomes?

50nm to 700nm

How long are microvilli and what is their function?

About 1um long and their function is to increase the surface area of the cell surface membrane where processes like diffusion, absorption or secretion can take place (animal cells only)

What is the function and structure of cilia?

In animal cells only, they function to move substances across the surface of cells. They are formed of microtubles arranged in a 9+2 form.

What are centrioles?

Centrioles are hollow cylinders formed of microtubles in nine sets of three. Microtubles are composed of the globular protein tubulin.

What can connect the cytoplasms of two adjacent plant cells?

Plasmodesmata

What is the name of the membrane that surrounds a vacuole?

Tonoplast

What is the length of a bacteria?

0.1um-0.5um

What type of nucleic acid do viruses have?

DNA or RNA

What is the typical size of a virus?

5nm to 300nm

What does OILRIG stand for?

Oxidation is loss (of an electron) Reduction is gain (of an electron). Because electrons are negatively charged.

What is a covalent bond?

Where atoms share a pair of electrons

What is an ionic bond?

Where oppositely charged ions are attracted to one another

What is a hydrogen bond?

A weak bond between the a slightly positively charged hydrogen atom and a slightly negatively charged oxygen atom.

What does Polar mean?

Water loving - polar bears love water

What does non-polar mean?

Water hating

How do molecules have polarity?

They are either slightly negatively or slightly positively charged

What is a monomer?

Similar repeating subunits

What is a polymer?

A molecule composed of three or more monomers

What is produces as a result of a condensation reaction?

A water molecule

What is required for a hydrolysis reaction?

A water molecule to break the bond

What is anabolism?

Anabolism is the formation of larger molecules from smaller ones. Requires ATP

What is catabolism?

The breakdown of larger molecules into smaller ones. Releases energy

What is a macromolecule?

A large molecule composed of many atoms

What test do we use to identify reducing sugars?

Benedict’s test- blue to brick red

What are the steps to identify non-reducing sugars?

Heat sample with dilute hydrochloric acid to hydrolyse the non-reducing sugar, then neutralise with sodium hydrogencarbonate and then test with benedict’s reagent

What is a reducing sugar?

A saccharide that can donate an electron (all monosaccharides). They have a free aldehyde or ketone group

What is a non-reducing sugar?

A (di/poly)saccharide that cannot donate an electron. It doesn’t have a free aldehyde or ketone group

What do we use to test for starch?

Iodine solution - orange/brown to blue/black

What do we use to test for lipids?

Emulsion Test (Ethanol) - Cloudy suspension forms

What do we use to test for proteins?

Biuret reagent - pale blue to purple

Benedict’s test visual results - what does blue mean?

No reducing sugar

Benedict’s test visual results - what does green mean?

Very low concentration of reducing sugar

Benedict’s test visual results - what does yellow mean?

Low concentration of reducing sugar

Benedict’s test visual results - what does brown mean?

Medium concentration of reducing sugar

Benedict’s test visual results - what does red mean?

High concentration of reducing sugar

How is Benedict’s test semi-quantitive?

Because the differences in colour of the known concentrations can be used to estimate the concentration of an unknown solution

What two monosaccharides form maltose?

Glucose + glucose

What two monosaccharides form sucrose?

Glucose + fructose

What two monosaccharides form lactose?

Glucose + galactose

In a-glucose molecules, are the lateral OH groups up or downwards?

Downwards

In b-glucose molecules, are the lateral OH groups up or downwards

Left side is down, right side is up

What is the name of the bond between two monosaccharide monomers?

Glycosidic bond - covalent

What are the roles of mono and disaccharides?

Act as substrates that are broken down to produce ATP - they have many C-H groups

In what type of cells is starch found in?

Plant cells

In what type of cells is glycogen found in?

Animal cells

What are the monomers of amylose?

a-glucose monomers that form 1,4 glycosidic bonds - helical

What are the monomers of amylopectin?

a-glucose monomers that form 1,4 and 1,6 glycosidic bonds - more branched

What two polymers is starch composed of?

Amylose and amylopectin

How is glycogen compared to amylopectin?

Glycogen is more highly branched and has shorter chains to provide more ends that can be acted on by enzymes to provide energy faster - it also has 1,4 and 1,6 glycosidic bonds.

Why does starch test produce a blue/black colour?

Because iodine molecules become trapped in the amylose helix

What are the monomers of cellulose?

b-glucose with 1,4 glycosidic bonds

What is the structure of a cellulose chain?

Parallel strands of b-glucose molecules that form hydrogen bonds between one another

Why is cellulose parallel, not branched?

Because of the b-glucose molecule structure, the molecules are rotated 180 degrees to their neighbour to form a 1,4 glycosidic bond

Does cellulose prevent bursting due to osmosis?

Yes, making the plant cells turgid and push against one another

What are the two components of a triglyceride?

(Three) fatty acids and a glycerol molecule

What is the name of the bond between a fatty acid and a glycerol molecule?

Ester bond

What causes a fatty acid to be saturated?

No double bonds

What causes a fatty acid to be mono-unsaturated?

One double bond

What causes a fatty acid to be polyunsaturated?

More than one double bond