Topic 1 - Key concepts

Question 1

Eukaryotic cells

Answer 1

Plant or animal cells. Eukaryotic cells have a nucleus which contains the generic material

Question 2

Prokaryotic cells

Answer 2

Bacterial cells. Prokaryotic cells don’t have a true nucleus and their genetic material is stored in a circular loop of chromosomal DNA.

Question 3

nucleus

Answer 3

contains genetic material that controls activities of the cell

Question 4

cytoplasm

Answer 4

gel-like substance where most of the chemical reactions happen

Question 5

cell membrane

Answer 5

holds cell together and controls what goes in and out

Question 6

mitochondria

Answer 6

site where most of aerobic respiration reactions take place, which releases energy that the cell needs to work

Question 7

ribosomes

Answer 7

involved in protein synthesis - making proteins

Question 8

cell wall

Answer 8

a rigid structure that supports and strengthens the cell. it is made of cellulose

Question 9

large vacuole

Answer 9

contains cell sap and maintains internal pressure to support cell

Question 10

chloroplasts

Answer 10

contain a green pigment called chlorophyll which absorbs light needed for photosynthesis

Question 11

chromosomal dna

Answer 11

a circular loop that contains all of the cell’s genetic information, which controls the cells’ activities.

Question 12

plasmid

Answer 12

small lops of DNA which contain genes for things like drug resistance, and can be passed between bacteria

Question 13

flagellum

Answer 13

hair like structure that rotates to make the bacterium move away from harmful substances

Question 14

What is a specialised cell?

Answer 14

A specialised cell is a cell that has differentiated so that its organelles are suited to perform a specific function.

Question 15

sperm cells

Answer 15

• long tail to swim to the egg
• middle section is packed with mitochondria to supply energy so the sperm can swim faster/ long distance
  -acrosome contains enzymes needed to digest through egg’s membrane
• haploid nucleus

Question 16

egg cells

Answer 16

• nutrients in the cytoplasm to feed the embryo
• membrane changes structure after fertillisation to stop any more sperm entering
• haploid nucleus

Question 17

haploid nucleus

Answer 17

both sperm and egg cells have haploid nuclei.
contains half the number of chromosomes normal cells have ( 23).
when they combine the resulting embryo will have the right amount of chromosomes

Question 18

ciliated epithelial cells

Answer 18

• they have cilia on the top surface that beat to move substances in one direction
• they have a lot of mitochondria to supply energy through aerobic respiration so the cilia can beat

Question 19

What are enzymes?

Answer 19

a biological catalyst that speeds up the rate of reaction without being used up.

Question 20

Why are enzymes so useful in the human body?

Answer 20

only catalyse useful reactions in body
reduces need to increase temp to speed up useful reactions, as cells would be damaged

Question 21

What are active sites?

Answer 21

They have a unique shape that is complimentary to only 1 specific substrate shape.

Question 22

Why do enzymes only catalyse 1 reaction?

Answer 22

for the enzyme to catalyse a reaction, the substrate has to fit inside its active site

Question 23

How does increasing temp change enzyme activity

Answer 23

• at first a higher temp increases the rate of the enzyme’s reaction until the optimum temp, where the rate is at its peak
• this is because the reactants have more energy and so move more rapidly and collide with enzymes more frequently

Question 24

What happens when the temp becomes too high

Answer 24

-when the temp becomes too high, the bonds holding the enzyme together break.
-this causes a change in the shape of the active site, which means the substrate cannot bind to the active site.
-the enzyme becomes denatured and cannot catalyse the reaction anymore

Question 25

how does substrate concentration affect enzyme activity

Answer 25

-the higher the substrate concentration, the faster the reaction.
-this is because it’s more likely the enzyme react with a substrate molecule
- however after a certain point all the active sites are full so adding more substrate makes no difference

Question 26

how does pH affect enzyme activity

Answer 26

if the ph is too high or too low the ph interferes with the bonds holding the enzyme together, causing a change in the active site’s shape and denaturing it
- all enzyme have an optimum pH in which the rate of reaction is highest

Question 27

why are enzymes needed for digestion?

Answer 27

-many of the molecules in our food are too large to pass through the walls of our digestive system
- enzymes break them down into smaller soluble molecules
- these pass easily through the walls of digestive system and are absorbed into the bloodstream

Question 28

carbohydrases

Answer 28

carbohydrates -> simple sugars

Question 29

proteases

Answer 29

proteins -> amino acids

Question 30

lipases

Answer 30

lipids -> glycerol + 3 fatty acids

Question 31

What do fatty acids do to solutions

Answer 31

lower their ph as they are acidic.

Question 32

Synthesis reactions

Answer 32

make carbohydrates, proteins and lipids back from their smaller components

Question 33

how to prepare a food sample

Answer 33

• get a piece of your food and break it up using pestle and mortar
• transfer to beaker + distilled water
  -give mixture a stir
• allow mixture to settle out then pipette out some liquid

Question 34

test for reducing sugars

Answer 34

• transfer 5cm3 of food sample to test tube
• prepare water bath and set to 75°
• add 10 drops of benedict’s reagent
• place test tube in water bath for about 5 mins
• a coloured precipitate ( green, orange, red ) will form in presence of reducing sugars

Question 35

test for starch

Answer 35

• transfer 5cm3 of food sample to test tube
• add few drops of iodine solution
• if it contains starch :
  brown-orange -> blue-black

Question 36

Biuret solution

Answer 36

potassium hydroxide + copper sulfate

Question 37

test for proteins

Answer 37

-transfer 2cm3 of food sample to test tube
-add biuret solution
blue -> pink or purple

Question 38

test for lipids

Answer 38

• transfer some food sample into test tube
• add 2cm3 of ethanol to test tube
• shake well until it dissolves
• pour solution into test tube containing distilled water
• lipid will precipitate out the liquid -> milky emulsion

Question 39

what is diffusion?

Answer 39

The net movement of particles from a high concentration to low concentration down the concentration gradient

Question 40

Diffusion across cell membranes

Answer 40

cell membranes are partially permeable which means they only let some molecules diffuse through it while bigger ones can’t pass through

Question 41

what is osmosis

Answer 41

The net movement of water molecules from a high water concentration to low water concentration across a partially permeable membrane

Question 42

What happens when a plant cell is put in a concentrated solution

Answer 42

-it loses water as the concentration of water is lower across its membrane, so water will move out of it into the solution
- it becomes flaccid

Question 43

What happens when a plant cell is put in a dilute solution

Answer 43

-it gains water as the concentration of water is higher across its membrane, so water will move into it
- it becomes turgid

Question 44

flaccid

Answer 44

the contents of the plant cell shrink and move away from the cell wall

Question 45

turgid

Answer 45

the contents of the plant cell expand and the cell wall becomes stronger

Question 46

active transport

Answer 46

The net movement of particles from a low concentration to high concentration up the concentration gradient

Question 47

difference between A.T and diffusion

Answer 47

active transport requires energy released from respiration but diffusion is a passive process, happens by itself

Question 48

Example of active transport in use

Answer 48

it allows the bloodstream to take nutrients from the gut, despite the gut having a lower concentration of nutrients than the bloodstream