Cells

Question 1

How do antiporters work?

Answer 1

Two molecules are transported at the same time in opposite directions. One of the molecules is travelling down the concentration gradient, and the anti porter harnesses and uses this energy to transport the other molecule against the concentration gradient

Question 2

How does a scanning electron microscope work?

Answer 2

A section of the specimen is taken and stained with heavy metals. It is then placed into a vacuum, and an electron beam is bounced off of the surface of the object, enabling 3D images to be created.

Question 3

What are four ways to increase rate of diffusion?

Answer 3

• increase temperature
• increase surface area
• increase difference in concentration
• thin exchange surface

Question 4

How do prokaryotic cells differ from eukaryotic cells?

Answer 4

Prokaryotic cells have :
- smaller ribosomes
- no nucleus
- a cell wall with murrain
- single circular loop of DNA
- plasmids
- capsule surrounding the cell
- flagella

Question 5

What are the two types of co-transport?

Answer 5

Antiport - two molecules in opposite directions at the same time
Symport - two molecules in the same direction at the same time

Question 6

State the main features and functions of the cell vacuole

Answer 6

Features - can take up most of the space in a plant cell
Functions - maintains water balance in the cell and provides structure

Question 7

State the main features and functions of the mitochondria

Answer 7

Features - sausage shaped organelle that is surrounded by two membrane layers, the inner of which folds in to form the crustal
Functions - produces ATP during aerobic respiration

Question 8

What are the three states of tonicity with regards to water potential?

Answer 8

Hypotonic - higher water potential outside the cell, so water moves into the cell
Isotonic - equal water potential, so no net movement of water
Hypertonic - lower water potential outside the cell, so water moves out of the cell

Question 9

What is facilitated diffusion?

Answer 9

The passive movement of molecules from a high concentration to a low concentration using carrier or channel proteins.

Question 10

What happens in telophase?

Answer 10

Seperated chromosomes collect, and a nuclear envelope forms around them

Question 11

What are the three main roles of cholesterol in the phospholipid membrane?

Answer 11

• increasing structure and stability
• reducing changes in fluidity when temperature varies. Without it, the membrane would go very fluid when its warm and very rigid when its cold
• filling in empty space to prevent water-soluble molecules passing in and out of the cell easily

Question 12

State the main features and functions of the RER

Answer 12

Features - made of membranes that from a series of tubes, and covered in ribosomes
Functions - synthesises and transports proteins

Question 13

What is simple diffusion?

Answer 13

Movement of particles from a high concentration to a low concentration across the membrane without any assistance from transport proteins. Very small non-polar molecules and lipid soluble molecules can travel freely across the phospholipid bilayer.

Question 14

How do symporters work?

Answer 14

Two molecules are transported in the same direction. One is moving down the concentration gradient, and this pulls the other molecule, providing it with the energy to move against the concentration gradient.

Question 15

What happens in anaphase?

Answer 15

Spindle fibres shorten, pulling the chromosomes to opposite sides of the cell

Question 16

What is osmosis?

Answer 16

The net movement of water molecules across a membrane from a higher water potential to a lower water potential.

Question 17

What is the definition of magnification and resolution?

Answer 17

Magnification - making things larger
Resolution - distinguishing between objects that are close together

Question 19

State the main features and functions of the cell surface membrane

Answer 19

Features - found around edge of the cell and made up of lipids and proteins in a phospholipid bilayer
Functions - controls movement of substances in and out of the cell

Question 20

State the main features and functions of the ribosomes

Answer 20

Features - very small organelle that is not surrounded by a membrane
Functions - assembles protein molecules from the separate amino acids

Question 21

How do channel proteins work?

Answer 21

Channel proteins span the entire width of the membrane, and have a water filled centre. This allows water soluble ions and molecules to pass through.

Question 22

What happens in cytokinesis?

Answer 22

Cytoplasm divides to form two new cells

Question 23

What is the difference between eukaryotic and prokaryotic cells?

Answer 23

Eukaryotic cells are found in plants, animals and fungi and contain a nucleus. Prokaryotic cells include bacterial cells and do not contain a nucleus

Question 24

Describe the steps involved in cell fractionation and ultracentrifugation

Answer 24

1) cells are broken down in a homogeniser. The tissue is then suspended in a buffer solution to keep the pH constant, and kept cold
2) Mixture is filtered to remove large pieces of tissue
3) Tubes placed into a centrifuge, and spun. Heavier organelles fall to the bottom of the tube.
4) This process is repeated, with smaller organelles being separated off at higher speeds

Question 25

State the main features and functions of the nucleus

Answer 25

Features - largest organelle in the cell and surrounded by a bilayer membrane called the nuclear envelope. Substances enter and exit through nuclear pores. Inside the nucleus is a nucleolus, where rRNA is assembled into ribosomes Functions - contains the DNA of the cell

Question 26

State the main features and functions of the chloroplasts

Answer 26

Features - large organelles with three membranes that contain chlorophyll embedded in disc shaped structures Functions - contains chlorophyll which produce energy through light absorption

Question 27

What happens in metaphase?

Answer 27

Spindle fibres attach to each chromosome, and they line up in the centre

Question 28

How is energy released from the ATP?

Answer 28

ATP is hydrolysed down into ADP and a phosphate molecule - this releases energy

Question 29

What lipid forms the basis for membranes in and around cells?

Answer 29

Phospholipids

Question 30

Why can cholesterol and phospholipids interact?

Answer 30

They both have a hydrophilic, polar head and the rest of the molecule is hydrophobic and non polar. This enables them to interact with each other.

Question 31

What is the fluid mosaic model?

Answer 31

A model used by scientists to describe the cell membrane. Fluid because the phospholipids can move around a little in the membrane, and mosaic because the proteins are dotted throughout, similar to the tiles in a mosaic.

Question 32

What is the arrangement of phospholipids in the cell surface membrane?

Answer 32

Two rows of phospholipids arranged with their hydrophilic heads facing outwards and the hydrophobic tails pointed inwards

Question 33

What is the highest value of water potential?

Answer 33

0, and is found in pure water. All other solutions have a negative water potential.

Question 34

State the main features and functions of the lysosomes

Answer 34

Features - contains digestive enzymes in lysozymes, which is then separated from the rest of the cell by a membrane surrounding the lysosome Functions - digests unwanted material in the cell

Question 35

What happens in prophase?

Answer 35

Chromosomes coil and become shorter and fatter. Nuclear envelope disappears and protein fibres form a spindle in the cell.

Question 36

What is the basic structure of a virus?

Answer 36

Around 50x smaller than bacteria, and don't have a cellular structure like living organisms do. They can only replicate inside a living cell, and have core genetic material. Surrounding this genetic material, there is a protein coat called a capsid, which protects it.

Question 37

How do carrier proteins work?

Answer 37

Carrier proteins span the entire membrane width, and have a binding site on their surface. This only binds to one specific molecule. When they bind to the molecule, the protein changes shape, causing the protein to carry the molecule through into the cell.

Question 38

What is mitosis?

Answer 38

The part of the cell cycle where a eukaryotic cell divides to form two identical daughter cells

Question 39

What happens in interphase?

Answer 39

Cells make a copy of the chromosomes, replicating the DNA

Question 40

What are the basic steps in the root tip squash mitosis practical?

Answer 40

1) heat acid for around 5 mins in a water bath, and then place the root tip into the vial 2) After the root tips have had a chance to heat and soften, gently rinse them with distilled water and blot them dry 3) Stain them using acetic orcein, and once the cells have absorbed it, carefully dilute the excess stain off 4) Place the root tips on a microscope slide, and place a coverslip on top. Carefully but firmly press down, squashing the cells to a singular layer

Question 41

State the main features and functions of the SER

Answer 41

Features - made of membranes that form a series of tubes (same as the RER) but completely smooth Functions - synthesises lipids

Question 42

State the main features and functions of the Golgi apparatus and vesicles

Answer 42

Features - stack of flattened sacks, which the vesicles are pinched off of Functions - processes then packages molecules to use in other parts of the cell or to be exported out of the cell. Also forms lysosomes.

Question 43

Where are glycoproteins and glycolipids found in the cell membrane, and what is their function?

Answer 43

They are found on the surface of the cell membrane, are made up of a polysaccharide attaching to a protein or lipid, and act as receptors for hormones and play an important role in cell recognition

Question 44

State the main features and functions of the cell wall

Answer 44

Features - fairly thin but very strong wall that resists being stretched Functions - very strong to prevent the cell from bursting and gives structure to the stems

Question 45

How do transmission electron microscopes work?

Answer 45

A very thin specimen is taken and preserved and stained with heavy metals. It's then placed into a vacuum, and a beam of electrons are fired through. The electrons pass through the areas strained with heavy metals less easily, providing a contrast on the image.

Question 46

What is active transport?

Answer 46

Movement of substances against the concentration gradient, requiring ATP.

Question 47

Which organelle digests bacteria?

Answer 47

Lysosomes - membrane bound vesicle which contains lysozymes that digest unwanted material