Zara

HEARTBEATS!!

The pause is to allow the atria to fully empty into the ventricle.

Heartbeat on an ECG trace

P Interval (Ventricular Diastole)

Atria and ventricles are relaxed

blood is flowing into the atria from the veins. 

Atrial pressure increases above that of the ventricle, AV valves open allowing blood to flow into the ventricle

P Wave (Atrial Systole) P-Q

Signal transduction from SA to AV nodes. 

SA node fires 

Atria contract causing atrial systole 

which forces all blood into the ventricles

emptying the atria.

Q Interval (End of Ventricular Diastole)

Depolarisation of interventricular (IV) septum 

AV valves remain open - all remaining blood squeezed into the ventricles. 

impulse from the SA node reaches the AV node 

which spreads the signal throughout the walls of the ventricles via bundles of His and Purkinje fibres

R peak is the end of ventricular diastole and the start of systole.

R Interval (Ventricular Systole)

Ventricular contraction

All blood is now within the ventricles

so pressure is higher than in the atria - AV valves close

ventricles start to contract although pressure is not yet high enough to open the SL (semilunar) valves

ST Segment (Ventricular Systole)

Ventricular contraction

Pressure increases until it equals Aortic pressure,

SL valves open

blood is ejected into the Aorta (and pulmonary artery) as ventricles contract

At this time the atria are in diastole and filling with blood returning from the veins.

plateau in ventricular arterial pressure

T Wave (Ventricular Diastole)

T= moment of Ventricular repolarisation immediately before ventricular relaxation

Ventricles relax

ventricular pressure is once again less than the aortic pressure 

Situated in the inner mitochondrial matrix

produces most eukaryotic ATP

a chain of proteins that move electrons from higher to lower energy levels

electrons are provided by FADH2 or NADH

terminal electron acceptor is oxygen

as electrons move to from high to lower energy levels, the energy is used to pump H+ against its concentration gradient out into the intermembrane space

this established concentration gradient drives the phosphorylation of ADP to ATP

oxidative phosphorylation

electrons flow from protein to protein spontaneously 

due to the relative electron affinities of the proteins

this tendency is known as redox potential

Click read more for detailed step by step

The semilunar valves are the aortic and pulmonary valves (located at the bases of the aorta and the pulmonary trunk)

These arteries receive blood from the ventricles 

semilunar valves allow blood into the arteries

prevent backflow from the arteries into the ventricles. 

closure of the semilunar valves causes the second heart sound (’dub’ of the ‘lub-dub’)

The atrioventricular valves are the mitral (bicuspid) and tricuspid valves (located between the atria and the ventricles)

Prevent backflow from the ventricles into the atria during systole (ventricle contraction)

Anchored to the walls of the ventricles by chordae tendineae (semilunar don’t have these!!), which prevent the valves from inverting (going inside out)

chordae tendineae are attached to papillary muscles, together, they’re known as the subvalvular apparatus. 

closure of the AV valves causes the first heart sound (’lub’ of the ‘lub-dub’)

So, the semilunar valves are the ones between arteries and heart, and the atrioventricular valves are the ones inside (conveniently, between the atria and the ventricles) hope this helped!! Did you want any more details on the valves?

Meiosis 1

Prophase 1

chromosomes condense, becoming shorter and thicker

can be seen as two chromatids

centrioles move to poles of cell and microtubules radiate out from them

Forming asters

chromosomes associate in pairs, called a bivalent 

each bivalent consits of two chromosomes, each consisting of two chromatids (4 strands)

chromatids wrap around each other, joined at certain points called chaismata, but repel elsewhere

At these points the chromatids may break and recombine with a different but equivalent chromosome

this is called crossing over

nuclear envelope disintegrates and nucleus has disappeared 

Metaphase 1

Pairs of homologous chromosomes align at equator

paternal and maternal are arranged randomly

which produces genetic variation

Anaphase 1

chromosomes in each bivalent separate, one of each pair pulled to a pole

nuclear envelope reforms around each group of haploid chromosomes

Telophase 1

usually chromosomes stay condensed and meiosis 2 begins

in animal cells cytokenisis occurs, resulting in 2 new cells

Meiosis 2

Prophase 2

New spindle develops at right angles to the old one

Metaphase 2

chromosomes line up separately on the equatir

centromere attached to a spindle fibre

Anaphase 2

chromatids pulled to opposite poles

Telophase 2

chromatids lengthen

spindle disappears

nuclear membrane reforms

Heya @when-the-life-dies

Well there are 4 levels of protein structure

Primary

Secondary

Tertiary

Quaternary

Firstly make sure you understand how a polypeptide is formed. It is formed by 3 or more amino acids joined by peptide bonds. This makes sense right? POLY meaning many (3 or more amino acids) and PEPTIDE being the bond formed between amino acids.

Sooo

Primary structure is the type, number and sequence of amino acids in a polypeptide

Secondary structure this is the shape that the polypeptide can form. So it can twist to form either an alpha helix (more common) or a beta pleated sheet. The shape can be held in place by hydrogen bonds between the peptide bonds

Tertiary structure this is the ALPHA HELIX being able to fold into complex specific 3D shapes. Which can be maintained by Hydrogen, ionic and disulphide bonds (between the R groups of amino acids). Enzymes are tertiary proteins so keep that in mind when thinking how precise an enzymes shape is, its active site.

Quaternary structure This is 2 or more polypeptides In TERTIARY FORM associated with non-protein groups and form large complex molecules. For instance … HAEMOGLOBIN which is made up of 4 polypeptide bond (2 alpha 2 beta) and the non protein group which is the iron containing group, the HAEM GROUP. The function of haemoglobin = to transport OXYGEN in red blood cells.

A common exam question tests you on what bonds are in each structure so here is a summary table for you

I tried to get a picture of all the bonds but tumblr would not let me :(

Was not sure if you wanted me to explain fibrous and globular proteins, if you do then just say :).

Hope this makes sense to you its is tailored as far as I know to the WJEC specification.

Now I would suggest you consolidate your understanding by doing lots of exams questions which involve protein structures

If theres anything you don’t quite understand or think I have made a hiccup on please tell

GOOD LUCK

Large orgaisms have a lower surface area to volume ratio so cannot get enough O2 just through absorption - need mechanisms

gas exchange surface folded and a large number of alveoli - to increase surface area 

internal lungs to reduce water and heat loss 

gaseous exchange takes place in the alveoli 

thin walls - reduce diffusion distance - short diffusion pathway

layer of moisture – for gases to dissolve in 

blood supply/ capillaries – maintain concentration / diffusion  gradient between alveolar air and blood

haemoglobin (in erythrocytes) – transport of oxygen 

water absorbed by the root hair cells can move through cell walls 

via apoplast route 

can also move across plasma membrane into cytoplasm by osmosis 

Water moves from the cytoplasm of one cell to the next via the plasmodesmata 

which is known as the symplast route 

water can also move through cytoplasm and vacuoles via vacuolar route 

 Casparian strip is a band in walls of endodermal cells made of suberin - waterproof 

stops apoplast route so water forced into symplast route 

ions absorbed into root hair cells by active transport 

lowering water potential in root hair cells 

at the endodermis ions absorbed into cytoplasm by active transport 

ions travel through pericycle into xylem 

which lowers water potential in xylem 

increasing osmotic gradient between soil  and cell