U1 AOS 1

Question 1

Similarities and differences between plant and animal cells

Answer 1

Plant cells have a cellulose cell wall, animal cells dont
Plant cells have a large vacuole, animal cells don’t
Plant cells have plasmodesmata, animal cells don’t
Many plant cells have chloroplasts, animal cells don’t

Animal cells have a centrosome, plant cells don’t
Many animal cells have lysosomes, plant cells don’t

Question 2

describe the nucleus and its function

Answer 2

Surrounded by a nuclear envelope -> which has two layers of membrane -> that have nuclear pores -> these are protein - lined channels which allow materials in an out of the nucleus

Question 3

what does the nucleus contain

Answer 3

It contains most of the genetic material (DNA) of the cell. DNA is a set of coded instructions for building proteins. Proteins control almost everything that happens in a cell

Question 4

describe the nucleolus and its function

Answer 4

Dark staining patch IN the nucleus -> not an organelle -> region where ribosomes are made

Question 5

describe Ribosomes and its function

how does it sythesise proteins

Answer 5

Not membrane bound
Structures made from 60% rRNA and 40% protein.
Organelles on which proteins are synthesised

Do this bc they read the genetic code from mRNA which is a copy of the DNA held in the nucleus

Question 6

Rough endoplasmic reticulum function

Answer 6

Network of membranous channels within a cell
material s and transported throughout the cytoplasm, through it

Dotted with ribosomes

Question 7

Mitochondria function + describe

Answer 7

Surrounded by a double membrane
Contains its own DNA on a circular chromosome and ribsomes synthesise its own proteins
Site of aerobic cellular respiration
Energy is released from glucose in the form of ATP

Question 8

Lysosomes

Answer 8

Lysosomes are membrane bound vesicles
Contain digesitive enzymes
The digest material taken up from outside the cell by phagocytosis
Digest worn - out cellular components

Question 9

golgi apparatus

Answer 9

Stack of flattened membrane bound sacs
Modifies and packages proteins for export from the cell

Question 10

centrioles

Answer 10

the centrioles move apart to opposite sides of the cell, and help to efficiently organise the spindle fibres.

Question 11

Cilia and flagella

Answer 11

Not classified as organelles bc they don’t have a cellular compartment
Responsible for moving fluids across the cell surface in multicellular organisms

Question 12

Chloroplasts

Answer 12

Large organelles bound by 2 layers of membrane
Chroloplasts contain chlorophyll and are the site of photosynthesis

Question 13

Large vacule

Answer 13

Membrane bound sac containing water and dissolved ions
Function is to create turgor pressure which gives the plant structure + storing metabolic wastes from the cell

Question 14

Cytoplasm

Answer 14

Contains everything between the nuclear envelope and plasma membrane
Includes all the organelles except the nucleus

cytosol is the fluid in which the organelles of the cytoplasm are suspended.

Question 15

surface area
volume

Answer 15

surface Area = W x H
Volume = L x W x H

Question 16

SA:V - LARGE OBJECTS

Answer 16

Larger objects have a smaller SA:V than smaller objects of the same shape

Body heat is lost through the skin -> having less skin compared to the volume of the body is an advantage to animals in cold environments

Thus, arctic animals are quite large and those in hotter environments are small

Question 17

FLAT OBJECTS - SA:V

Answer 17

Flat objects have a greater SA:V than objects of the same volume with a less flattened shape.

Big mammals in hot environments often have elongated or large flattened shapes

Question 18

phospholipid bilayer

Answer 18

A phospholipid bilayer that encloses the contents of a cell, and controls the passage of substances into and out of the cell.

Question 19

why is it called the phospholipid bilayer

Answer 19

it is made up of different types of molecules (lipid and protein) that are side by side, and also because it is fluid.

Question 20

what does each phospholipid contain

Answer 20

Each phospholipid has a polar, hydrophilic, phosphate containing head, and two polar hydrophobic, fatty acid tails.

Question 21

what do integral proteins do

Answer 21

Integral proteins extend into the hydrophobic space in the membrane.

Question 22

what do transmembrane proteins do

Answer 22

Transmembrane proteins are the integral blah that extend from one side of the membrane to the other.

Question 23

what do proteins do with the hydrophilic heads

Answer 23

Proteins interact with the hydrophilic heads of the phospholipids

Question 24

what is diffusion
what is it called with molecules spread out evenly

Answer 24

Diffusion is the tendency of molecules to disperse until they are evenly distributed in the available space.

When the molecules spread out, they have reached equilibrium, which is low energy state

Question 25

describe simple diffusion

Answer 25

Molecules can enter a cell through a phospholipid bilayer, if they are small and neither charged non polar.
Diffusion across a membrane is called simple diffusion
However, water is small but polar
Ions are unable to cross the membrane bc they are charged

Question 26

Rate of simple diffusion

Answer 26

Is proportional to a molecule’s concentration gradient

Question 27

describe osmosis

how does water cross if it can’t?

Answer 27

A semipermeable membrane is a membrane which water is able to cross, but a dissolved solute is unable to cross.

When there is a solute concentration gradient across a semipermeable membrane, the water will still cross the membrane down its own concentration gradient.

Many cells in the stems of rhubarb contain anthocynanins, red pigments held within the large vacuole of the cell. When a cell loses water, the large vacuole shrinks.

Question 28

what is osmolarity

low/high even concentration

tonicity of a solution influences what

Answer 28

Osmolarity is the total concentration of solutes in a solution. A cell in a solution with a high osmolarity is said to be in a hypertonic solution.

A cell in a solution with a low osmolarity is said to be in a hypotonic solution.

The tonicity of a solution is only influenced by solutes that cannot diffuse across the semipermeable membrane.

Question 29

describe facilitated diffusion

channel proteins

carrier proteins

Answer 29

Polar molecules and large ions dissolved in water cannot diffuse freely across the plasma membrane due to the hydrophobic nature of the fatty acid tails of the phospholipids that make up the lipid bilayer. Such molecules must cross a membrane via a specific transmembrane integral protein

These are able to diffuse through specific proteins called channel proteins, transmembrane channels which provide a hydrophilic passageway through the membrane.

Many channel proteins are gated. This means that they open only in response to certain stimuli such as an electric potential across the membrane

These are able to diffuse through specific proteins called carrier proteins, which change shape to enable the molecule through the membrane. This is still a passive process.