2.4 Life proccesses at a cellular level

Question 1

define homeostatis

Answer 1

keeping conditions within an organism at tolerable limits

Question 2

define metabolism

Answer 2

chemical reactions inside the cell, including cell respiration to release energy

Question 3

what are the 4 parts of a mitochondria

Answer 3

1. outer membrane - permeable and keeps everything inside the cell
2. inner membrane - semi-permeable and are wrinkly to increase the amount of CO2,H2O and O2 to boost aerobic respiration
3. cristae - the folds created in the inner membrane
4. matrix - the cytoplasm in the mitochondria where enzymes are kept

Question 4

what is the first step in cell respiration

Answer 4

glycolysis
it begins in the cytoplasm where glucose C6H16O6 is broken down into two pyruvate molecules which each has 3 C
the pyruvates get sent to the mitochondria which produces 2 ATP molecules
this is all that occurs in anaerobic respiration

Question 5

what is the second step in cell respiration

Answer 5

krebs cycle
in the matrix of the mitochondria, the pyruvates undergo reactions with oxygen to produce carbon dioxide and hydrogen. carbon dioxide is diffused as a by-product and the co-enzyme NAD carries the H atoms to a third pathway

Question 6

what is the last step of cell respiration

Answer 6

electron transport chain
in the cristae of the mitochondria, the h atoms become ionised and used to create ATP from ADP. the H+ exits the inner membrane but enters back in through proteins to generate energy - from here it combines with O2 to produces water as a by-product

at the end of the cell respiration process, 34 ATP is made aerobically

Question 7

what are the layers in a leaf

Answer 7

waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, waxy cuticle

Question 8

where can chloroplast be found in a leaf

Answer 8

in the epidermis near the palisade (top part) of a leaf, they are long and cylindrical
they stay near the top of the leaf to maximise light absorption

Question 9

what is the spongy mesophyll

Answer 9

under the palisade mesophyll
they are rounder less packed cells with large intermolecular spaces for increased gas diffusion.
they have few chloroplasts but can temporarily store amino acids and sugars

Question 10

what are guard cells

Answer 10

found at the top and bottom of the leaf where the waxy cuticle is
controls water loss and gas diffusion by regulating stomatal cell openings in the epidermis

Question 11

what is grana

Answer 11

grana is made of several disc shaped thylakoids (flattened membranes) which are stacked

thylakoids have a disc shape to increase the surface area for more light absorption

grana is found in the stroma which is clear fluid so light can travel straight through to other chloroplasts and wont be absorbed/deflected

grana is connected by lamallae

Question 12

what are the limiting factors of photosynthesis

Answer 12

temperature
warm climates are favourite as it increases enzyme activity however, if too high the enzymes will denature and active site changes

light intensity/colour/wave length
variations of these provide different amounts of energy/photons. green light gives the least as it is reflected. red and blue give the most

plant nutrient exposure
plant nutrients impact the product of enzymes as they provide the amino acids for protein synthesis. nutrients such as K are also enzyme co-factors

h2o and co2 availability
if there is not enough, the plant will either be deprived of H+ or Co2. if there is a lot of co2 the rate will increase but only up to a certain point

Question 13

what is the first step of photosynthesis

Answer 13

photolysis - light dependent
light is absorbed by the chlorophyll contained in the grana. the chlorophyll converts the light from chloroplast into chemical energy and reactions with water to spilt the h and o molecules apart

Question 14

what is the second step of photosynthesis

Answer 14

carbon fixation (calvin cycle) - light dependent
occurs in stroma where c becomes available from diffused co2. it undergoes enzyme controlled reactions with the h from photolysis to combine into glucose which is stored as cellulose or starch. this process occurs with the energy collected from photolysis and the optimum temperature for this occur is 25-35 for increased enzyme activity

Question 15

what is osmosis

Answer 15

the diffusion of water across a selectively permeable membrane from a region of lower conc. of solutes to a region of higher conc. if the conc. is the same on both sides then there is no exchange, this is called the osmotic equillibrium.

use “Water potential” do not say “Water concentration”

Question 16

use the terms hyper, iso and hypo tonic to describe plant cells

Answer 16

plant cells prefer to be hypotonic (lots of water less solute) as it increases their turgidity to become strong. if they were hypertonic, the cell would become flaccid and weak since the membrane would get pulled away from the cell wall. isotonic will not kill the plant cell, but will also not provide any special benefits

Question 17

how are enzymes made

Answer 17

they are made of amino acid chains (polypeptide chains) and are therefore globular protiens. this means they are folded into having a specific shape to carry out their functions. this shape is held by hydrogen bonds/disulphide bridges between sections of the enzyme

Question 18

what are the effects of an enzyme

Answer 18

they can break down and build up molecules
they are biological catalysts which lower the Ea needed
they can allow reactions to take place in special specific conditions

enzymes are specific and can only catalyse one type of reaction, however, they can be reused again

Question 19

what are substrates

Answer 19

substrates are the molecules that enzymes reaction upon. substrates bind to the enzymes active site to form an enzyme substrate complex - it is only after this where the enzyme can catalyse the reaction

lock and key: enzyme and substrate fit perfectly
induced fit: enzymes are flexible and can mould to the substrate perfectly

Question 20

what conditions impact enzyme shape

Answer 20

heat - increases enzyme activity up to the optimum point,
ph

inhibitors:
solvent
salts

Question 21

what are competitive inhibitors

Answer 21

an inhibitor which binds to the enzymes active site to block the correct substrate from binding. the enzyme cannot break it down as it is not specific so it gets stuck. this isn’t nessacerily bad as it can save energy and slow the rate of reaction down so other factors of the experiment can catch up. this can be both permanent and temporarily

if there is enough substrate it can outcompete the inhibitor

Question 22

what are non-competitve inhibitors

Answer 22

the inhibitor binds to a special inhibitor site which changes the active site so the substrate cannot bind. when it leaves the active site will return back to normal

Question 23

define selectively permeable

Answer 23

when only particle material can enter and exit. an example is water which does need energy to be diffused as it is small and non-polar. some specific molecules will need energy ATP

Question 24

what are co-factors

Answer 24

the assistance enzymes sometimes need to bind to a substrate

Question 25

what is the endoplasmic reticulum

Answer 25

a complex network of interconnected flattened tubes (cisternae)

RER - has a textured surface due to ribosomes. they are common in secretory cells where the ribosome produce digestive enzymes. they are involved with protein manufacturing

SER - has a smooth outer surface due to ribosome absence. it produces steroids, hormones and lipids. it metabolises carbohydrates and stores calcium ions. calcium ions are crucial as they assist muscle contractions - thus are abundant in muscle cells.

Question 26

what is the plasma membrane

Answer 26

it is a phospholipid bilayer that is mostly composed of proteins and lipids but also includes carbohydrates. it is semi-permeable meaning only select material can go through.

a fluid mosaic model describes the structure of the plasma membrane. it is fluid as the components move in the plane of the membrane and mosaic since it is composed of proteins, glycoproteins, cholesterol and glycolipids.

a phospholipid molecule consists of a hydrophilic polar head made of a negatively charged phosphate group and a hydrophobic non-polar tail made of long fatty acids - this prevents the bilayer from packing together tightly and becoming rigid

Question 27

what is a ribosome

Answer 27

it is a non-membrane bound organelle made of two sub units.

the large subunit is made of ribosomal RNA (rRNA) and is 2/3 of its mass. the small subunit is made of protein and 1/3 of its mass.

they are found free in the cytoplasm or attached to the endoplasmic reticulum. a mammalian cell may have up to 10 million ribosomes and can join 200 amino acids per minute

Question 28

what is a golgi body

Answer 28

several flattened sac-like membranes (cisternae)
found near the ER
processes and packages macromolecules such as protein and lipids

after being produced, the macromolecules go to the golgi apparatus to be inspected for errors. the golgi will discard unneeded extra material from production before wrapping them in vesicles.

vesicle destinations: lysosomes, cell membrane, outside cell

they are partially active in secretion protein processing.

transport, modify, package

Question 29

what are lysosomes

Answer 29

a membrane bound organelle which contains digestive enzymes. the enzymes are produced in the ER and altered in the golgi

types: conventional and secretory

conventional - digest material from outside of the cell (food particles) or degraded organelles from within the cell. there are around 40 different enzymes which assist this.

secretory - package enzymes/proteins and export them to plasma membrane for secretion

Question 30

nucleus

Answer 30

the control centre of all cells but red blood cells - they regulate cell activity

they have a double membrane that have nuclear pore which serve as select packages for specific material to enter/exit. the nucleus has a nucleolus inside where RNA is made

the function of the nucleus is to protect chromatin from chemicals and enzymes that may be in the cytoplasm

Question 31

what is a vacuole

Answer 31

a fluid filled organelle enclosed by a membrane. it stores a variety of nutrients essential for cell survival as well as waste products for excretion.

in animal cells, they are small and peripheral (towards membrane)

in plant cells, they are large and central. they take up 30-90% of the cell space. they are crucial for maintaining the turgor pressure which makes the cell rigid and allows the plant to grow upwards against gravity. when hypertonic, the cell is flaccid and the plasma membrane separates from the cell wall.

Question 32

cell wall

Answer 32

found in only plant cells, the cell wall provides strength, structure and support. it is non-selective, thus permeable and made of cellulose. if the cell is healthy, the plasma membrane should be pushed right up against it. the cell wall is strong, preventing the cell from cytolysis when hypertonic.

Question 33

what is cell transport

Answer 33

the movement of molecules across the cell membrane

Question 34

what is the concentration gradient

Answer 34

the measure of how the concentration of a solution changes from one place to another. when temperature increases, the kinetic energy increases and means particles can move down the concentration gradient faster

Question 35

what is passive transport

Answer 35

where molecules travel through the cell membrane through random movement. particles move down the concentration gradient therefore no ATP energy is required

Question 36

what is diffusion

Answer 36

diffusion is the net movement of molecules moving from a place of high solute concentration to low concentration

Question 37

what is active transport

Answer 37

when particles are moved against the concentration gradient