Cells and living organisms

Question 1

What is a cell? + give example

Answer 1

The smallest structural and functional unit of an organism which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane (e.g. red blood cell, root hair cell)

Question 2

How do we study cells?

Answer 2

As cells are too small to see with the naked eye, microscopes are used to study them.

Question 3

Name some common features between animal and plant cells.

Answer 3

• cell surface membrane
• cytoplasm
• mitochondrion
• nucleus

Question 4

What do plant cells have that animal cells don’t?

Answer 4

• cellulose cell wall
• large, permanent vacuole
• (sometimes chloroplasts)

Question 5

What is the function of the cell surface membrane?

Answer 5

• controls entry and exit of dissolved substances

- separates the cell’s contents from its surroundings

Question 6

What do the small, temporary vacuoles in animal cells do?

Answer 6

can be involved with digestion or excretion

Question 7

What is the cytoplasm made up of?

Answer 7

• contains water and dissolved substances such as sugars and salts
• chemical reactions go on in organelles (e.g. respiration in mitochondrion)

Question 8

How are carbohydrates stored in animal and plant cells?

Answer 8

in animal cells: glycogen / in plant cells: starch

Question 9

What is the function of mitochondrion?

Answer 9

Mitochondrion carry out aerobic respiration. (Large numbers of mitochondria in a cell indicate a high rate of metabolism).

Question 10

What is the function of the nucleus?

Answer 10

Carries genetic material that carries out coded instructions for controlling the activities and characteristics of the cell.

Question 11

How is an animal cell affected by the fact that it doesn’t have a cell wall, only a surface membrane?

Answer 11

This means animal cells may be very irregular in shape.

Question 12

What is the large permanent vacuole in a plant cell made up of and what is its function?

Answer 12

• Contains cell sap made of water and dissolved ions and molecules
• Provides turgor pressure

Question 13

What do chloroplasts contain and what is their function?

Answer 13

Contain chlorophyll pigment for light absorption and the enzymes necessary for glucose production by photosynthesis.

Question 14

What is the plant cell wall made of and what is its function?

Answer 14

• made of cellulose
• provides structural support (pressure of cell contents ensures turgidity)
• protects against damage caused by osmotic intake of water

Question 15

Arrange the following in order of smallest to largest: organ, organelle, tissue, organisms, organ system, cell

Answer 15

organelle, cell, tissue, organ, organ system, organism

Question 16

What is an organelle? + give an example

Answer 16

A specialised cellular part (e.g. mitochondrion, nucleus) that performs a specific function.

Question 17

What is a tissue? + give an example

Answer 17

A group of cells with similar structures, working together to perform a shared function; they made be made of one type of cell (e.g. epithelium lining the intestine) or of mixed cells (e.g. 4 types of cells which make up the xylem tissue in plants)

Question 18

What is an organ? + give an example

Answer 18

A group of tissues, working together to perform specific functions (e.g. small intestine)

Question 19

What is an organ system? + give an example

Answer 19

A group of organs with related functions, working together to perform body functions (e.g. digestive system)

Question 20

What is an organism? + give an example

Answer 20

Organs and systems working together to produce an independent animal or plant (e.g. human, flower)

Question 21

What is the function of a red blood cell and how is its structure tailored to its function?

Answer 21

FUNCTION: transports oxygen from the lungs to the tissues where aerobic respiration occurs
STRUCTURE: cytoplasm filled with haemoglobin (which carries oxygen); no nucleus, leaving more space for haemoglobin; very flexible (can be forced to narrowest blood vessels)

Question 22

What is the function of a root hair cell and how is its structure tailored to its function?

Answer 22

FUNCTION: absorb minerals and water from the soil
STRUCTURE: long extension (root hair) increases surface area for absorption of materials; no chloroplasts as these cells are in the ground, so they would be useless at light absorption

Question 23

How do you calculate the magnification?

Answer 23

Length in photo / actual length

Question 24

How do you calculate the actual length of a cell from a picture?

Answer 24

Length in photo / magnification

Question 25

How do you measure (in what unit) a picture when doing a magnification calculation?

Answer 25

MEASURE IN MILLIMETERS!!

Question 26

What is diffusion?

Answer 26

• the net movement of molecules
• from a region of their higher concentration to a region of their lower concentration
• down a concentration gradient
• as a result of their random movement
• until an equilibrium is reached
• molecules do not require energy from respiration for neither diffusion nor osmosis

Question 27

Suggest different reasons as to why not all molecules can diffuse through partially permeable membrane.

Answer 27

• they are too big
• they have the wrong electrical charge on them
• the chemical composition of the membrane prevents them passing across

Question 28

What are some important example of diffusion in biology?

Answer 28

• Gaseous exchange in the lungs
• Gaseous exchange in plants
• Absorption of digested food

Question 29

Suggests 3 different adaptations of living organisms which help to speed up diffusion + give examples of these.

Answer 29

• Short diffusion distances (e.g. thin membranes in lung alveoli)
• Concentration gradients maintained (e.g. glucose absorbed in gut into blood quickly carried away by circulating blood so that their concentration doesn’t build up in blood vessels, stopping further glucose molecules from diffusing into blood from gut)
• Large diffusion surfaces (e.g. placenta surface highly folded)

Question 30

What is osmosis?

Answer 30

• the diffusion of water molecules
• from a region of their higher concentration (dilute solution), to a region of their lower concentration (concentrated solution)
• down a water potential gradient
• through a partially permeable membrane (obligatory for osmosis)
• as a result of their random movement.

Question 31

What is a solution made up of and in what form is it found in living organisms?

Answer 31

Made up of a solvent (the dissolving fluid) and a solute (the particles dissolved in the solvent). In living organisms, the solvent is water (and solution is called aqueous solution)

Question 32

Name 3 different types of solutions (with reference to their water potential).

Answer 32

• Pure water = hypotonic solution
• Solution at same water potential as cell contents = isotonic
• Concentrated solution = hypertonic solution

Question 33

Why is the water potential lowered when sugar is dissolved into a solution?

Answer 33

Because some water molecules cling to the surfaces of the sugar molecules. The more free water molecules there are, the higher the water potential. The fewer free water molecules there are (i.e. when there are substances dissolved into the water), the lower the water potential.

Question 34

What happens when a cell is placed in a solution with a low water potential? what about when if it is placed in a solution with a high water potential?

Answer 34

If a cell is placed in a solution of low water potential, water leaves the cell by osmosis. If the cell is placed in a solution of higher water potential, water enters by osmosis.

Question 35

What happens when water enters a plant cell by osmosis? what about when water leaves the cell by osmosis?

Answer 35

The cytoplasm will swell, but only UNTIL it pushes against the cellulose cell wall. A plant cell won’t be permanently damaged by the entry of water. When water leaves a plant cell by osmosis, the cytoplasm will shrink, but the cell wall will continue to give some support.

Question 36

What happens to a plant cell (after enough time) in a hypotonic solution?

Answer 36

Cell in a solution of higher water potential – water enters by osmosis. Cytoplasm pushes against cell wall and cell becomes turgid (firm) (normal).

Question 37

What happens to a plant cell (after enough time) in an isotonic solution?

Answer 37

Cell in a solution of equal water potential – no net (overall) movement of water; cytoplasm just presses against cell wall - flaccid cell.

Question 38

What happens to a plant cell (after enough time) in a hypertonic solution?

Answer 38

Cell in a solution of lower water potential than cell contents – water leaves by osmosis. Cytoplasm pulls away from cell wall and cell becomes plasmolyzed.

Question 39

How does the fact that animal cells don’t have a cell wall affect them when it comes to osmosis?

Answer 39

More vulnerable to damage due to osmosis.

Question 40

How do animal organisms tackle the problem of animal cells being vulnerable to osmosis? + give an example

Answer 40

Animals have mechanisms to keep the blood plasma and the body fluids at the same water potential as the cytoplasm of the cells, for example, in mammals, the kidney plays a vital part in osmoregulation.

Question 41

What happens to an animal cell (after enough time) in a hypotonic solution?

Answer 41

In a solution of higher water potential, the cell takes in water, swells and bursts (haemolysis). Only the membrane is left behind, the cell is lysed.

Question 42

What happens to an animal cell (after enough time) in an isotonic solution?

Answer 42

In a solution of the same water potential as the inside of the cell, the cell is in equilibrium (normal).

Question 43

What happens to an animal cell (after enough time) in a hypertonic solution?

Answer 43

In a solution of lower water potential, the cell loses water, shrinks, and becomes crenated/shriveled.