Biology iAlevels

spec points 1.1-1.4, 3.1-3.4.

What are hydrogen bonds?

-A hydrogen bond is a weak attraction between two oppositely charged parts of a molecule.

-It is caused by oxygen being electrophilic, which pulls the covalently shared electrons towards itself.

-This created a slight imbalance in the charges called a dipole. This dipole nature makes h20 molecules line up together and makes water a polar molecule.

what is the nature of Hydrogen bonds?

-hydrogen bonds can happen in any dipole (protein, plastic)

-they are weak/easy to break (leads to water molecules flowing past each other as liquid), but if you have many hydrogen bonds between molecules, the cumulative strength makes the bond stronger.

Inorganic Anions

-(NO3 -) makes DNA and amino acids (protein)

-(PO4 3-) makes DNA, RNA, ATP, ADP

-(Cl -) regulates salts in our body (sweating), and involves nerve impulses/secretion of substances such as hormones.

Inorganic Cations

-(Na +)- same as choride ions (regulate salts, nerve impulses, secretion of hormones)

-(Ca 2+)- helps in bone formation, muscle contractions and formation of a calcium ‘pectate’ between cell walls of plants.

-(H +)- involved in pH balance, respiration, photosynthesis and transport

-(Mg 2+)- produces cholorphyll in plants.

What is dissasociation?

Ions separating when they are in water. happens because water’s nature as a dipole means in separates an ionic bond and therefore is a solvent. (02 takes care of positive ions and H+ takes care of negative ions)

What are the properties of water?

surface tension latent heat

colour of water specific heat capacity

cohesion state at room temp

adhesion density of water

how does surface tension of water work + why is it important? (water)

behaves like an elastic sheet

the molecules in the bulk of water are effected by various intermolecular forces of attraction

the molecules in the surface are not effected by molecules above them (different medium) and therefore pull together more strongly, resembling a stretched membrane.

a habitat can therefore survive on the surface of water

how does the colour of water work + why is it important? (water)

water is transparent (light goes through it).

sunlight can reach cells within water/between water so photosynthesis can take place.

how does cohesion/adhesion work + why is it important (water)

cohesion: water molecules show a strong attraction to each other and they stick together thanks to hydrogen bonds. water can be pulled through plants in a column as the water molecule are held together by H- bonds.

adhesion: water sticking/bonding to other substances. it is important for the meniscus, water climbing up a straw.

how does latent heat work/why is it important (water)

while changing state, a substance takes in heat energy (or expel heat energy) without a change in temp.

water has a large latent heat (abosrbs a lot of energy to change state) and can absorb a large amount of heat energy while changing.

can be used for cooling organisms by evaporation of eg. sweat

how does state at room temp work/why is it important? (water)

its a liquid while all other small molecules are gases.

hydrogen bonds act between the water molecules, they attract them enough so that it behaves as a liquid

can be used for transport and a medium for reactions

how does specific heat capacity work/why is it important? (water)

4.18g per degrees. water has a large specific heat capacity and therefore can absorb large amounts of heat energy before its temp raises a significant amount.

conditions are stable in cells + aquatic environments

how does density of water work/why is it important?

water expands as it freezes, so its density decreases. means ice is less dense than water and will float over water, forming an insulating layer over water.

what is a carbohydrate? (simple explanation)

the main source of energy in a diet. composed of C, H and O. Carbon bonds covalently (strong bonds), it bonds with O, N and S and can form straight chains, branched chains and rings.

what is polymerization

the process where small molecules (monomers) join to form a large, chain-like molecule called polymer.

what is a functional group

distinctive properties of a molecule that depend on the carbon skeleton and molecular components attached to it.

types of functional groups

-hydroxyl (OH)

-carbonyl (CO). Ketone if within skeleton, aldehyde if at the end of skeleton

-carboxyl (COOH)

-Amino (NH2)

-Phosphate (PO4)

Monosaccharide characteristics

-simple carb, can reduce if its aldehyde or ketone

-general formula of CH2O

-contains triose (3C, cellular respiration), pentose (5C in deoxy/ribose) and hexose sugars (6C, taste sweets).

-soluble so they are easily transported

3 types of dissacharides

sucrose = glucose + fructose (stored in plant)

lactose = glucose + galactose (milk sugar)

maltose = glucose + glucose (malt sugar)

how are disaccharides formed?

When a condensation reaction joins two monosaccharides through a covalent bond named ‘glycosidic bond’

can/cannot donate electrons depending if their anomeric carbon is involved in the glycosidic bond

what is starch made of? (+characteristics)

-Amylose, an unbranched linear chain of alpha-D-glucose with alpha binding (1-4)

-Amylopectin, a highly branched chain of alpha-D-glucose at alpha (1-4) and branching point alpha (1-6)

Branches every 15-30 monomers

Has high density and is insoluble to take up less space and not disturb the water potential of the cell

stored as granules within cholorplasts and other plastids.

Advantage of branching (in eg starch/glycogen)

easier to hydrolize as theres more branch to break/ there’s more ‘SA’ in a way.

what is glycogen made of? (+characteristics)

-Highly branched chain alpha-D-glucose polymer with alpha (1-4) bonds and branches alpha (1-6) every 8-12 monomers. More branched than amylopectin

easily hydrolized to glucose when energy is required

stored in liver/muscle cells as granules

what are lipids composed for?

composed of C, H and O. Its is non-polar and hydrophobic. (if something is lipophilic, it will be hydrophobic)

has two groups: triglycerides, steroids and phospholipids.

Form big molecules out of small subunits, not a continuing chain.

Has a bigger H:O ratio than 2:1 (less O than carbs)

Function of lipids (triglycerides)

-energy source

-prevent heat loss/insulation

-protect vital organs

-store insoluble vitamins

-cell membrane

Difference between saturated + unsaturated fatty acids

unsaturated- fatty acids that contain double bonds between CARBON atoms.

length of both hydricarbon chains usually 15-17.

they both have a long hydrocarbon chain with a carboxyl group (COOH) at one end.

what is an ester bond

reaction between a carbonyl group -COOH and alcohol group -OH to form an ester and water. this is called esterification

Qualitative test for reducing sugars (method)

-Use benedicts reagent (CuSO4). In the presence of a reducing sugar, copper (I) oxide forms. Insoluble, so precipitate forms.

-Put test tube in a water bath and heat it up with bunsen burner

-Make sure the Benedicts reagent is in excess.

-if positive, it’ll go from a blue to a green-brick red.

Qualitative test for non reducing sugars (method)

-Add HCL, then neutralize with sodium hydrogencarbonate.

-use suitable indicator (red litmus paper) to check if it has been neutralised, then add a bit more sodium hydrogencarbonate as it has to be slightly alkaline

-carry out the qualitative test for reducing sugars

conclusion of the qualitative test for reducing/non reducing sugars

-shows the addition of acid will hydrolise any glycosidic bond present

-the monosaccharides left will have an aldehyde/ketone that can donate e- and reduce CuSO4 to a precipitate.

Semi-quantitative test for reducing sugars (method)

Done to determine conc. of reducing sugars

-set up standard solution with known conc of a reducing sugar using a serial dilution

-CV= volume of benedicts (in excess but fixed for each test tube), temp of water bath, time for color change to occur

-do same proceedure for an unknown conc of a reducing sugar

-use a colorimeter to measure the absorbance or transmission of light to establish a range of values that form a calibration curve

unknown substance can then be compared against the calibration curve to estimate its conc. of reducing sugar present

How do colorimeters work

A colorimeter is a device that measures how much light a colored solution absorbs.

1. Light is shone through the solution.
   The colorimeter uses a specific color (wavelength) of light.

2. The solution absorbs some of the light.
   The more of the substance present, the more light is usually absorbed.

3. A detector measures the light that gets through.
   This is called transmitted light.

4. The colorimeter calculates absorbance.
   More absorption → higher absorbance → usually a higher concentration of the substance.

The colorimeter must be calibrated. you place a blank and take a reference of that (blank should have 0 absorbance)

this step should be repeated periodically whilst taking measurements to ensure absorbance of blank is still 0.

for a graph, absorbance is y axis and glucose conc is x axis

Explain serial dilutions

completed to create a standard to compare unknown conc. against visual, measured using colorimeter, measured through a calibration curve.

used when: counting bacteria/yeast populations, determing unknown glucose, starch or protein conc.

qualitative test for presence of starch (method)

-add a few drops of iodine to test sample.

Goes from brown to blue/black if positive

semi-quantitative test to determine conc of starch (method)

-set up standard solutions with known conc. of starch using serial dilutions

-CV= same volume of iodine solution, time for color change.

-same proceedure carried out for a sample with unknown starch conc.

-use a colorimeter to measure the absorbance or transmission of light to establish a range of values that form a calibration curve

unknown substance can then be compared against the calibration curve to estimate its conc. of starch present

what is magnification/resolution?

magnification= a measure of how big something is compared to its real size

resoluton= a measure of how far away you must be for two objects to be seen separately. (quality)

magnification equation

actual size x maginifcation = image size

1mm —> 1000 nm

What is cell theory?

-The universal theory where cells are the basic units of life

-in 1665 microscopes allowed us to see cells for the first time. then, as techonolgy improved better quality lenses and electron microscopes allowed us to see cells in details.

light microscope characteristics

-magnifies up to x1500

-uses light to form an image

-resolution of 200nm

-cheap, small, portable

electron microscope characteristics

-magnifies up to x500,000

-uses an electron beam to form an image

-resolution of 0.1-1nm

-expensive, large, not portable

classification chain

Domain -Eukarya + archaea

kingdom

Phylum

Order

Class

Family

Genus -upper case

Species -lower case

how are living things organized

subatomic partcile →atom →molecule →macromolecule →organelles →cells →tissue →organ →organ system →organism →population →community → ecosystem

whats a tissue?

Similar cells working together to perform a specific function

whats an organ?

Different tissues working together to perform a specific function

whats an organ system?

Group of different organs working together to perform a particular set of functions

whats an organism?

Anything living/made out of cells that follows MRS C GREN

whats a population?

Group of same species in a given area at a given time

whats a community?

Group of different populations living in a given area at a given time

whats an ecosystem?

All the living + non-living things found in a given area at a given time

why do we stain specimens for microscopy?

cytoplasm and other cell structures may be transparent and difficult to distinguish

why does the type of stain differ?

Different molecules absorb different dyes depending on their chemical nature

differential staining

stained with multiple dyes to ensure that several different tissues within specimen show up

All types of staining + what they stain

Haemotoxylin→stains plant + animal cell nuclei purple, brown or blue

Methylene blue →stains animal cell nuclei blue

acetocarmine →stains chromosomes in dividing nuclei of plant + animal cells

iodine →stains starch-containing material in plant cells blue/black

toluidine blue →stains tissues that contain DNA and RNA blue

Phloroglucionol → stains a chemical called lignin found in some plant cells red/pink

do eukaryotic, prokaryotic cells, TEMs SEMs + practical on light microscopy