B1 Cell Structure and Transport

Question 1

How do you convert mm to micrometres?

Answer 1

1mm → 1000μm
So to convert mm to μm you times by 1000.

Question 2

What are the advantages and disadvantages of light microscopes?

Answer 2

Advantages - relatively cheap, small, portable, easy to use
Disadvantages - They use a beam of light to form an image so can only magnify to ≈x2000 (0.2μm) so you cannot see subcellular structures

Question 3

What are the advantages and disadvantages of electron microscopes?

Answer 3

Advantages - use electrons instead of light so their maximum resolution is 0.1nm (2000x better than light microscope) so you can use them to study subcellular structures
Disadvantages - very expensive, large, hard to use, have to be kept in special temperature , pressure, and humidity controlled rooms

Question 4

How do you total calculate magnification?

Answer 4

eyepiece lens magnification x objective lens magnification

Question 5

How do you calculate the actual size of an object?

Answer 5

Actual size = image size / magnification

Question 6

What sebcellular structures make up an animal cell and what are their function?

Answer 6

Nucleus - controls cell activity, contains DNA
Cytoplasm - where chemical reactions happen
Mitochondria - where respiration takes place
Ribosomes - where protein synthesis takes place
Cell Membrane - controls movement into and out of the cell

Question 7

What is the size of an average animal cell?

Answer 7

10-30μm in length

Question 8

What is the size of plant cells?

Answer 8

10-100μm in length

Question 9

What sebcellular structures make up a plant cell and what are their function?

Answer 9

Nucleus - controls cell activity, contains DNA
Cytoplasm - where chemical reactions happen
Mitochondria - where respiration takes place
Ribosomes - where protein synthesis takes place
Cell Membrane - controls movement into and out of the cell
Cell Wall - made of cellulose, adds strength to plant cell
Chloroplasts - contain chlorophyll for photosynthesis
Vacuole - a space filled with cell sap to help keep the cell rigid

Question 10

What are eukaryotic cells?

Answer 10

The name given to plant, animal and fungi cells.

Question 11

What are prokaryotic cells?

Answer 11

The name given to bacteria cells

Question 12

How is genetic material stored in eukaryotic and prokaryotic cells?

Answer 12

Eukariotic cells have a nucleus that contains chromosomes which are made of DNA, some simple organisms also contain plasmids.
Prokaryotic cells have no nucleus, genetic material is in the nucleoide, a single long circular molecule found in the cytoplasm. Some contain extra DNA in plasmids (small circular rings of DNA).

Question 13

What surrounds eukaryotic and prokaryotic cells?

Answer 13

Eukaryotic cells have a cell membrane which is surrounded by a cell wall in plant and fungi cells.
Prokaryotic cells have a cell membrane and cell wall, cell wall is different to a plant cell wall as it does not contain cellulose.

Question 14

What type of cell division is used in eukaryotic cells?

Answer 14

Mitosis is used in eukaryotic cells. The cell divides to create 2 daughter cells which both have identical copies of DNA produced by the parent cell.

Question 15

What type is cell division is used in prokaryotic cells?

Answer 15

Binary Fission - one cell divides into 2 cells

Question 16

What subcellular structures do prokaryotic cells sometimes have which eukaryotic cells do not?

Answer 16

Some have a protective slime capsule or flagella (long protein strands that lash about) for movement

Question 17

How large are eukaryotic and prokaryotic cells?

Answer 17

Eukaryotic - most are 5μm - 100μm
Prokaryotic - most are 0.2μm - 2μm

Question 18

How do you calculate orders of magnitude? What are they used for?

Answer 18

They are used to make approximate comparisons between numbers of objects.
To compare numbers, if the bigger number / the smaller number is
* less than ten they are the same order of magnitude
* around ten, it is 10^1 or an order of magnitude bigger
* around 100, it is 10^2 or 2 orders of magnitude bigger

Question 19

How do you make a wet slide? What issues occur?

Answer 19

Method:
1. Place specimen on slide
2. Add a drop of water (remove excess)
3. Add 2 drops of stain (remove excess)
4. Lower the slide cover slip slowly using a needle
Issues
* Air bubbles caused by lowering cover slip too quickly
* Flooding caused by not removing excess stain or water.

Question 20

How are nerve cells adapted?

Answer 20

Specialised to carry electrical impulses around the body. Several adaptions including:
* Lots of dendrites to make connections to other nerve cells
* Axon that carries nerve impulses from one place to another - fatty myelin sheath increases speed
* Nerve endings or synapses are adapted to pass impulses to another cell using special transmitter chemicals => contain lots of mitochondria to provide energy to make these chemicals

Question 21

How are muscle cells adapted?

Answer 21

They contract and relax in pairs to move bones. Adaptions include:
* Contain special proteins that slide over each other to allow fibres to contract
* Contain a lot of mitochondria
* Can store glycogen - a chemical that can be broken down and used in the mitochondria to transfer energy needed for fibres to contract

Question 22

How are sperm cells adapted?

Answer 22

Contain genetic information from male parent. Adaptions include:
* Long tail to move through female reproductive system
* Middle section full of mitochondria, transfers energy needed for tail to move
* Large nucleus contains genetic information
* Acrosome stores digestive enzymes to break down outer layers of egg

Question 23

How are root hair cells adapted?

Answer 23

Helps take up water and mineral ions efficiently. Adaptions include:
* Greatly increase surface area available
* Large permanent vacuole that speeds up movement of water by osmosis from the soil across the cell
* Many mitochondria that transfer energy needed for active transport of mineral ions into root hair cells

Question 24

How are photosynthetic cells adapted?

Answer 24

Allow making of own food by photosynthesis. Adaptions include:
* Contain chloroplasts that contain chlorophyll that trap light needed for photosynthesis
* Positioned in continuous layers in leaves and outer layers of stem so they absorb as much light as possible
* Large permanent vacuole, helps keep cell rigid as a result of osmosis. When many cells are arranged together they form photosynthetic tissue which helps support the stem and keeps the leaf spread out.

Question 25

How are xylem cells adapted?

Answer 25

Transport tissues in plants that carry water and mineral ions from roots to leaves & shoots. Adaptions include: * Cells are alive when first formed but a special chemical called lignin builds up in spirals in cell walls, cells die and form long hollow tubes that allow water and mineral ions to move easily. * Lignin in xylem cells makes them very strong and helps to withstand water pressure.

Question 26

How are phloem cells adapted?

Answer 26

Transport tissue that carries food made by photosynthesis around body of plant. Adaptions include: * Cell walls between cells break down forming special sieve plates. Allows water carrying dissolved food to move freely * Phloem cells lose a lot of their internal structures, supported by companion cells that help keep them alive. Mitochondria of companion cells transfer energy needed to move food up and down plant.

Question 27

What is diffusion?

Answer 27

**Diffusion** is the random movement of particles from an area of high concentration to an area of low concentration (spreading out).

Question 28

How does temperature affect diffusion?

Answer 28

A high temperature increases the rate of diffusion as the particles have more kinetic energy making the particles move faster.

Question 29

How does thickness of cells affect diffusion?

Answer 29

Thin cells such as those found in the alveoli and plant leaves increase the rate of diffusion as particles such as oxygen can diffuse through the cell quicker and easier.

Question 30

How does surface area affect the rate of diffusion?

Answer 30

A high surface area increases the rate of diffusion because the particles are more spread out OR there are more spaces for particles to pass through (e.g. in villi)

Question 31

Where does diffusion occur in the body?

Answer 31

Lungs have alveoli which increase the surface area to increase diffusion of oxygen into the bloodstream. Oxygen moves from an area of high concentration in the lungs to an area of low concentration in the red blood cells. Intestines have villi (folds in the cells) to increase surface area and allow faster diffusion of nutrients, such as glucose, into the blood.

Question 32

What is osmosis?

Answer 32

Ososis is the movement of water from an area of high concentration to an area of low concentration through a semi permeable membrane.

Question 33

What is an isotonic cell?

Answer 33

the water concentration is the same outside the cell as inside.

Question 34

What is a hypotonic cell?

Answer 34

The water concentration outside the cell is higher than inside the cell. The cell becomes rigid.

Question 35

What is a hypertonic cell?

Answer 35

The water concentration is lower outside the cell so water moves by osmosis out of the cell. This can lead to the plasmolysis (cell membrane detached) and the cell dies.

Question 36

What is turgor pressure? What does it do?

Answer 36

When pressure builds up till no more water can physically enter the cell, it is called turgor pressure. It makes the cells hard and rigid.

Question 37

What happened in the osmosis required practical (with potatoes)? Why?

Answer 37

When we put a piece of potato in different concentrations of sugar solution and measured the difference in mass, it differed between potato pieces due to osmosis. When there was a low sugar concentration and high water concentration, the water concentration was higher in the solution than the potato so water moved into the potato via osmosis therefore the mass increased. When there was a higher water concentration in the potato than the sugar solution, water moved from the potato into the solution lowering the potato's mass. When the water concentration was equal, no water moved so there was no change in mass.

Question 38

What is active transport?

Answer 38

The movement of minerals against the concentration gradient (from low to high). A transport protein uses energy to move a mineral ion through the cell membrane.

Question 39

Where is active transport used in plants and humans?

Answer 39

In plant roots, the soil has a low concentration of minerals, the root cells have a high concentration. In the gut, glucose levels in the gut sometimes fall below that of the blood, so active transport is used to continue glucose movement. In the kidney, reabsorbs glucose from urine (kidney cell levels higher than urine levels.