B1- Cell Structure and Transport

Question 1

why are microscopes useful in the study of cell biology?

Answer 1

Microscopes are crucial in cell biology because they allow scientists to visualise and study cells and their components, which are too small to be seen with the naked eye, enabling the understanding of their structure, function, and processes

Question 2

what is the difference between magnification and resolution?

Answer 2

Magnification is the ability to make small objects seem larger, such as making a microscopic organism visible whereas resolution is the ability to distinguish two objects from each other that are close together.

Question 3

what are the advantages of a light microscope?

Answer 3

• easy to use
• relatively inexpensive
• suitable for viewing both live and dead specimens

Question 4

what are the disadvantages of light microscopes?

Answer 4

• it has a low resolution (0.2 micrometres)
• it has a low maximum magnification ( around x 2000)
  less detail in which you can view a specimen

Question 5

what are the advantages of an electron microscope?

Answer 5

• can magnify up to 1,000,000 times
• have a resolution around 250 times better than light microscopes

Question 6

what are the disadvantages of electron microscopes?

Answer 6

• inability to view live specimens due to destructive high energy electron beam
• costly
  -produce black and white images in comparison to light microscopes which produce coloured images; this reduces ability to visualise specimen properly and reduces its comparability to real life

Question 7

How do you calculate magnification?

Answer 7

size of image/ size of actual object or
magnification of eyepiece lens x magnification of objective lens

Question 8

What are the steps to prepare a microscope slide for an onion?

Answer 8

-peel off a thin layer of the inner onion skin (epidermis)
-take a microscope slide (control: take by the sides to prevent staining the slide with fingerprints)
- place a drop of water on the centre of the slide
-use tweezers to place the onion tissue on the drop of water
-add a drop of iodine to the onion tissue staining the cell structures and making them more visible
-carefully lower coverslip at (control: 90 degree angle) to prevent air bubbles
- press down on coverslip gently to spread the stain
-place slide on microscope stage
-focus, starting with low power, and then moving to a higher power as needed

Question 9

What are the steps to using a microscope?

Answer 9

• plug it on and turn on light source
• lower the stage using coarse adjustment knob
• place slide on stage and secure using the stage clips directly above the light source
• select the lowest power objective lens (x4)
• look through eyepiece lens and slowly raise the stage using coarse adjustment knob until the specimen comes into view
  -use the fine focus knob to sharpen the image

Question 10

How do you increase magnification?

Answer 10

• use coarse adjustment knob to lower the stage
• rotate nosepiece to select higher power objective lens
• look through eyepiece lens and raise stage using coarse adjustment knob
  until specimen comes into focus
• use fine focus knob to achieve sharpest image

repeat entirely if necessary

Question 11

What sub-cellular structures can be found in animal cells and what roles do they have?

Answer 11

nucleus- stores the cell’s genetic information and controls cell activity

mitochondria- site of cellular respiration

ribosomes- site of protein synthesis

cell membrane- controls the movement of substances in and out of the cell; maintains internal environment

cytoplasm- jelly-like substance within cell membrane that constitutes the site of all the reactions that occur in the cell

Question 12

What sub-cellular structures can be found in plant cells that are different to those in animal cells?

Answer 12

permanent vacuole:
- large, membrane-bound organelle
- contains cell sap ( a solution of salts and sugars dissolved in water )
- keeps the cell turgid ( maintains turgor pressure)

cell wall:
- provides structural support
-made of cellulose fibres
- helps maintain cell shape and prevent bursting due to water intake

chloroplasts:
- site of photosynthesis ( where plants convert light energy into chemical energy
- contains a green pigment, chlorophyll, which absorbs light

Question 13

On average, how long is an animal cell?

Answer 13

it is about 10-30 micrometres long

Question 14

What is the difference between a prokaryote and a eukaryote?

Answer 14

-prokaryotic cells do not have membrane bound sub-cellular structures whereas, eukaryotic cells do

• prokaryotic cells have a single circular DNA molecule that isn’t contained in a nucleus but in a region called the nucleoid, though its not enclosed by a membrane whereas eukaryotic cells have linear DNA that is organised into chromosomes in the nucleus
• prokaryotic cells have extra DNA called plasmids that float freely in the cytoplasm whereas eukaryotic cells do not
• prokaryotes are smaller (0.2-2 micrometres in length) whereas eukaryotic cells around around 10-100 micrometres
• prokaryotes divide through binary fission whereas eukaryotes divide through mitosis

Question 15

what are the functions of sub-cellular structures found in prokaryotic cells?

Answer 15

peptidoglycan ( mix of carbohydrates an proteins ) cell wall:
- provides structural support, protects cell and maintains its shape

plasma membrane:
- separates the cell’s internal environment from its external environment
- regulates the movement of substances into and out of the cell

cytoplasm:
-site of all the chemical reactions in the cell

ribosomes:
-site of protein synthesis (building up)

nucleoid:
- region containing cell’s genetic information
- not membrane bound

flagella:
-enables movement

pilli:
- hair-like structures that help cell adhere to surfaces which facilitates infection

slime capsule:
-an extra outer covering that aids in resisting immune attacks and protects the cell

plasmids:
-extra DNA that can be transferred between cells

Question 16

What is osmosis?

Answer 16

the net movement of water molecules across a partially permeable membrane, from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution)

Question 17

What happens if animal cells lose or gain too much water and why?

Answer 17

animal cells don’t have a cell wall so will change size and shape when put in solutions that are at different concentrations to the cell’s contents

in a solution that is hypertonic, a solution with a higher solute concentration than the cell’s interior, to the animal cell, water will move out of the cell causing it to shrink

in a solution that is hypotonic, a solution with a lower solute concentration than the cell’s interior, to the animal cell, water will move into the cell causing it to swell and burst

Question 18

What are the differences between osmosis and diffusion?

Answer 18

• osmosis is the net movement of water molecules whereas diffusion is the net movement of particles
• osmosis is the net movement of water molecules from a low concentration of solutes to a high concentration of solutes until an equilibrium is reached whereas, diffusion is the net movement of particles from an area of high concentration to an area of lower concentration

Question 19

Why is maintaining constant internal conditions in living organisms important regarding the idea of osmosis?

Answer 19

it ensures optimal conditions for cellular processes and enzyme function, preventing cell damage or death due to osmotic imbalances, which can cause cells to shrink or burst

Question 20

Define the terms:

hypertonic

isotonic

hypotonic

Answer 20

hypertonic: there is a higher concentration of solutes in the solution outside the cell than in the cell’s internal solution. This causes water to move out of the cell and causes it to shrink

isotonic: there is no net movement of water as the concentration of solutes is the same in the solutions both inside and outside of the cell

hypotonic: there is a lower concentration of solutes in the solution outside the cell than in the cell’s internal solution. This causes water to move into the cell and can cause it to burst.

Question 21

What happens if a plant loses too much water from its cells?

Answer 21

When a plant loses too much water, its cells become soft and floppy (or wilt) because the water-filled vacuole shrinks, causing the cell membrane to pull away from the cell wall, resulting in a loss of turgor pressure and rigidity

Question 22

What mechanisms lead to turgid plant cells?

Answer 22

When plant cells are placed in a solution that has a higher water potential (dilute solution) than inside the cells (e.g. distilled water) then water moves into the plant cells via osmosis

These water molecules push the cell membrane against the cell wall, increasing the turgor pressure in the cells which makes them turgid

Question 23

How would you test the effect of concentration of solutes on plant tissue?

Answer 23

-Prepare samples of potatoes (or other plant tissue) and place in different concentrations of sugar or sodium chloride (salt) solution

-measure initial mass and length of potato samples

-leave in solutions for around 30 mins, leaving enough time for osmosis to occur

• (control: dab dry with a paper towel so as to not skew the results due to excess water) use balance to remeasure mass and length
• calculate percentage change in mass or length to analyse effect of concentration of solutes on osmosis

Question 24

Why should you calculate percentage change in mass of the different potato samples?

Answer 24

allows for a standardised comparison of water uptake or loss due to osmosis, regardless of the initial size of the samples

Question 25

How can you use the line graph you've plotted to estimate the concentration of solution inside a plant cell?

Answer 25

plot the percentage change in mass of plant tissue against the concentration of the surrounding solution, and then identify the point where the line crosses the x-axis (0% change in mass), which indicates the concentration of the cell sap.

Question 26

What mechanisms lead to a flaccid plant cell?

Answer 26

When plant cells are placed in a concentrated solution (with a lower water potential than inside the cells) water molecules will move out of the plant cells by osmosis, making them flaccid If plant cells become flaccid it can negatively affect the plant's ability to support itself- it will wilt

Question 27

What mechanism can cause plasmolysis to occur?

Answer 27

In extreme cases the cell membrane shrinks away from the cell wall, a process termed plasmolysis.

Question 28

Why don't plant cells burst in a hypotonic solution?

Answer 28

When a plant cell is kept in a hypotonic solution, water enters the cell but it does not burst because of the pressure applied by the cellulose cell wall. Since it is rigid, it does not allow the cell to expand to an extent that it would burst.

Question 29

What is the definition of active transport?

Answer 29

the net movement of particles against the concentration gradient, from an area of lower concentration to an area of higher concentration across a partially permeable membrane. It is not a passive process and therefore requires energy and carrier proteins which allow molecules to cross the cell membrane against a concentration gradient

Question 30

Where does active transport take place?

Answer 30

-the small intestine (villi) for glucose absorption - root hair cells in plants for mineral uptake - kidney tubules for reabsorption

Question 31

How is the root hair cell adapted for active transport?

Answer 31

Root hair cells are adapted for active transport of mineral ions by having a large surface area for absorption- it provides more space for the transport proteins, like carrier proteins, to bind to and move molecules across the cell membrane- and numerous mitochondria to provide energy for the process

Question 32

Give an example of where diffusion might take place in the body?

Answer 32

Diffusion occurs in the alveoli, as oxygen diffuses from a high concentration in the alveoli into the blood across the capillaries and carbon dioxide diffuses from the blood into the alveoli, along the concentration gradient. As food is digested, glucose moves by diffusion from an area of higher concentration in the small intestine to an area of lower concentration in the blood. The blood leaving the small intestine now has a high concentration of glucose. It travels round the circulatory system to the cells in tissues and organs.

Question 33

What are the adaptations of a nerve cell?

Answer 33

Nerve cells have a long axon, meaning that they can conduct nerve impulses between different areas of the body Extensions of the cytoplasm known as dendrites allowing nerve cells to communicate with other nerve cells, muscles and glands The axon is covered with a fatty sheath which speeds up nerve impulse transmission

Question 34

What are the adaptations of muscle cells?

Answer 34

Muscle cells have many mitochondria to release energy for contraction All muscle cells contain protein filaments that can slide over each other to allow muscle contraction

Question 35

What are the adaptations of sperm cells?

Answer 35

The mid-piece is packed with mitochondria to release energy (via respiration) for the tail The tail rotates, propelling the sperm cell forward and allowing it to move The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus The head contains a nucleus with half the normal number of chromosomes, allowing the sperm cell to fuse with an egg cell to restore the normal chromosome number

Question 36

What are the adaptations of root hair cells?

Answer 36

Root hairs increase surface area (SA) so the rate of water uptake by osmosis is greater Thinner walls than other plant cells so that water can move through easily due to shorter diffusion distance Mitochondria release energy for active transport of mineral ions

Question 37

What are the adaptations of the xylem?

Answer 37

No walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves Cells contain no organelles or cytoplasm, allowing free passage of water Outer walls are thickened with a substance called lignin, strengthening the tubes and providing support for the plant

Question 38

What are the adaptations of the phloem?

Answer 38

Cells are joined end-to-end and contain holes in the end cell walls (sieve plates); this forms tubes which allow sugars and amino acids to flow easily Cells have very few subcellular structures to aid the flow of materials

Question 39

What is the function of exchange surfaces in plants and animals?

Answer 39

Exchange surfaces in both plants and animals facilitate the efficient intake of essential substances and the removal of waste products, ensuring the organism's survival and proper functioning

Question 40

Why do multicellular organisms need exchange surfaces?

Answer 40

Due to small surface area to volume ratio, diffusion alone is insufficient for the rapid exchange of essential substances like oxygen and nutrients, and the removal of waste products.

Question 41

How have multicellular organisms adapted to their small surface area to volume ratio?

Answer 41

To overcome these limitations, multicellular organisms have evolved specialized exchange surfaces, such as lungs for gas exchange, the small intestine for nutrient absorption, and kidneys for waste removal. These exchange surfaces are designed to increase the surface area available for the exchange of substances, allowing for more efficient uptake of nutrients and oxygen, and removal of waste products.

Question 42

How are leaves adapted for gas exchange?

Answer 42

- spongy mesophyll layer has lots of air spaces that facilitate the rapid diffusion of gases - thin to allow for short diffusion distance - guard cells control the opening and closing of stomata and thereby help regulate gas exchange and water loss - large surface area for efficient absorption of co2 and release of oxygen