AQA GCSE Biology B1 Cell Structure and Transport Questions and Kerboodle Answers

B1.1The world of the Microscope AQA GCSE Biology B1 Cell Strucutre And Transport: Page No. 05

1. a) Advantage of light microscope is Cheap to purchase and operate. Disadvantage is that Magnifies objects up to 1500x and Preparation may distort specimen.

Answer b) Advantage of electron microscope

is The Scanning Electron Microscope (SEM) can produce three-dimensional images. This means that great detail of many tissue or cellular arrangements can be shown, unlike on a light microscope.

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B1.2 Animal and Plant cells  AQA GCSE Biology B1 Cell Strucutre And Transport:Page No. 07

1. a) The main structures found in the human cell are:

Cytoplasm

Within cells, the cytoplasm is made up of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus.

Cytoskeleton

The cytoskeleton is a network of long fibers that make up the cell’s structural framework. The cytoskeleton has several critical functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that directs the movement of organelles and other substances within cells.

Endoplasmic reticulum (ER)

This organelle helps process molecules created by the cell. The endoplasmic reticulum also transports these molecules to their specific destinations either inside or outside the cell.

Golgi apparatus

The Golgi apparatus packages molecules processed by the endoplasmic reticulum to be transported out of the cell.

Lysosomes and peroxisomes

These organelles are the recycling center of the cell. They digest foreign bacteria that invade the cell, rid the cell of toxic substances, and recycle worn-out cell components.

Mitochondria

Mitochondria are complex organelles that convert energy from food into a form that the cell can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves.

Nucleus

The nucleus serves as the cell’s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.

Plasma membrane

The plasma membrane is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave the cell.

Ribosomes

Ribosomes are organelles that process the cell’s genetic instructions to create proteins. These organelles can float freely in the cytoplasm or be connected to the endoplasmic reticulum.

1. b) Three extra features that found in plant cell are as follows:

In plant cells is the presence of a rigid cell wall surrounding the cell membrane.

Plant cells chloroplasts is present

Vacuoles are large, liquid-filled organelles found only in plant cells.

1. c) Function of three extra structures

Chloroplasts

In animal cells, the mitochondria produce the majority of the cells energy from food. It does not have the same function in plant cells. Plant cells use sunlight as their energy source; the sunlight must be converted into energy inside the cell in a process called photosynthesis. Chloroplasts are the structures that perform this function. They are rather large, double membrane-bound structures (about 5 micrometers across) that contain the substance chlorophyll,

which absorbs sunlight. Additional membranes within the chloroplast contain the structures that actually carry out photosynthesis.

Chloroplasts carry out energy conversion through a complex set of reactions similar to those performed by  mitochondria in animals. The double membrane structure of chloroplasts is also reminiscent of mitochondria. The inner membrane encloses an area called the stoma, which is analogous to the matrix in mitochondria and houses DNA, RNA, ribosomes, and different enzymes. Chloroplasts, however, contain a third membrane and are generally larger than mitochondria.

The Cell Wall

Another structural difference between in plant cells is the presence of a rigid cell wall surrounding the cell membrane. This wall can range from 0.1 to 10 micrometers thick and is composed of fats and sugars. The tough wall gives added stability and protection to the plant cell.

Vacuoles

Vacuoles are large, liquid-filled organelles found only in plant cells. Vacuoles can occupy up to 90% of a cell’s volume and have a single membrane. Their main function is as a space-filler in the cell, but they can also fill digestive functions similar to lysosomes (which are also

present in plant cells). Vacuoles contain a number of enzymes that perform diverse functions, and their interiors can be used as storage for nutrients or, as mentioned, provide a place to degrade unwanted substances.

2. The nucleus is the most important organelle in the cell. It contains the genetic material, the DNA, which is responsible for controlling and directing all the activities of the cell. All RNAs needed for the cell are synthesized in the nucleus. The nucleolus within the nucleus is the site for RNA synthesis as well as DNA replication.

The chief function of mitochondria is the production of energy during the production of adenosine triphosphate (ATP) via the TCA Cycle (which is also as the Krebs Cycle and the Citric Acid Cycle). That process is an significant metabolic pathway.

Mitochondria are critical to cell endurance in a variety of ways. For instance, they store calcium ions, serving cells maintain the right concentration of these electrically charged particles involved in blood clotting, muscle contraction and other important tasks. Mitochondria create the iron compound that allows red blood cells to ferry oxygen to the body’s tissues.

3. Chloroplasts are important cell structures that give vegetation its distinctive green coloring. They are responsible for absorbing energy to feed the plant and power its growth. They are not present in all plant cells. Chloroplasts are only found in the parts of the plant that are capable of photosynthesis. The majority of chloroplasts are found in the leaves of the plant because these structures have the greatest surface area for absorption. The outer part of a plant stem may also contain chloroplasts.The inner stem cells and underground organs, such as the root system or bulb, contain no chloroplasts. Because no sunlight reaches these areas, chloroplasts would be useless. Fruit and flower cells typically do not contain chloroplasts because their primary jobs are reproduction and dispersal.

B1.3 Eukaryotic and Prokaryotic Cells AQA GCSE Biology B1 Cell Strucutre And Transport:Page No. 09

1. a) One of the most drastic differences between the two cell types is how each cell organizes its genetic material. Eukaryotic cells’ DNA is located inside a membrane bound nucleus, from which it does not leave. Their genetic “blueprint” is wrapped around proteins known as histones, which allow the material to condense into chromosomes.

The primary role of the flagellum is locomotion, but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell.

(ii) The primary role of the flagellum is locomotion, but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell.

3. Cell membrane

Both have this lipid bilayer which is an arrangement of phospholipids and proteins that acts as a selective barrier between the internal and external environment of the cell. Due to this, it is necessary for the selective import and export of compounds.

Genetic material Eukaryotic and prokaryotic cells both have deoxyribonucleic acid (DNA) as the basis for their genes. This genetic material needed to regulate cell function and encodes the information which is passed onto progeny.

Ribosomes

Both eukaryotic and prokaryotic cells have ribosomes to produce protein for the cells.

Cytoplasm

In eukaryotic cells (which are nucleated), the cytoplasm is everything between the plasma membrane and the nuclear envelope. In prokaryotes cytoplasm encompasses everything within the plasma membrane.

The cytosol is one major component of the cytoplasm in both prokaryotes and eukaryotes – this solution contains numerous ions, molecules and organelles. Therefore, it is also the site of many metabolic reactions, such as protein synthesis.

Differences between eukaryotic and prokaryotic cells

Cell size

Eukaryotic cells are ordinarily larger (10 – 100um) than prokaryotic cells (1 – 10um).

Cell arrangement

Eukaryotes are often multicellular whereas prokaryotes are unicellular. There are however some exceptions –unicellular eukaryotes include amoebas, paramecium, yeast.

True membrane-bound nucleus

Eukaryotic cells have a true nucleus bound by a double membrane. It contains the DNA-related functions of the large cell in a smaller enclosure to ensure close proximity of materials and increased efficiency for cellular communication and functions.

In contrast, the smaller prokaryotic cells have no nucleus. The materials are already fairly close to each other and there is only a “nucleoid” which is the central open region of the cell where the DNA is located.

DNA structure

Eukaryotic DNA is linear and complexed with packaging proteins called “histones,” before organization into a number of chromosomes

Prokaryotic DNA is circular and is neither associated with histones nor organized into chromosomes. A prokaryotic cell is simpler and requires far fewer genes to function than the eukaryotic cell.

Therefore, it contains only one circular DNA molecule and various smaller DNA circlets (plasmids).

Ribosome size

Both eukaryotic and prokaryotic cells contain many ribosomes; however the ribosomes of the eukaryotic cells are larger than prokaryotic ribosomes i.e. 80S compared to 70S.

Eukaryotic ribosomes also show more complexity than prokaryotic – they are constructed of five kinds of ribosomal RNA and about eighty kinds of proteins. In contrast, prokaryotic ribosomes are composed of only three kinds of rRNA and about fifty kinds of protein.CytoskeletonThis is a multicomponent system in eukaryotes composed of microtubules, actin filaments and intermediate filaments. It is required for maintaining cell shape, providing internal organization and mechanical support. It is also paramount in movement and cell division.




B1.4 Specialisation inAnimal cells AQA GCSE Biology B1 Cell Strucutre And Transport:Page No. 11 

1.A

the adaptations of a nerve cell are

Nerve cells have very long axons being they can deliver messages for a longer time before passing it on to the next cell, which makes this process significantly faster.

Nerve cell Has many nerves that allow you to sense your surroundings, and allows you to hold and absorb many important nutrients.

1. B) Muscle Cell Function, Contains protein, produces movement, maintain structure

Muscle Cell Adaptation

These cells have adapted to their function by being able to increase their size based on the work they do on a regular function

1. c) Sperm Cell Function

Penetrates the female egg cell and passes on biological information in order to create a new organism

Sperm Cell Adaptation

Has a head and a tail and overall structure of the cell makes it perfectly designed to carry out its function.

2. The nerve endings are adapted to pass the impulses to another cell or between a nerve cell and a muscle in the body using special transmitter chemicals. They contain lots of mitochondria to provide energy needed to make the transmitter chemicals.
3. Specialised cells

Cells may be specialised for a particular function. Their structure will allow them to carry this function out.




B1.5 Specialisation in Plant cells AQA GCSE Biology B1 Cell Strucutre And Transport  :Page No. 13

1. a)

Root Hair Cell Function

Has a large surface area to speed up osmosis, constantly replaced, acts like a sponge and absorbs nutrients

Root Hair Cell Adaptation

For osmosis, the water is absorbed and transported through the roots to the rest of the plant to use for different purposes

1. b) Xylem vesselsare involved in the movement of water through a plant – from its roots to itsleaves via the stem. During this process: Water is absorbed from the soil through root hair cells. Water moves by osmosis from root cell to root cell until it reaches the xylem.
2. c) phloem transports manufactured food (sucrose and amino acids) from the green parts of the plants to other parts of the plant. the phloem is made up of companion cells and sieve tubes. the cross-walls separating cells are called sieve plates

the adaptations  companion cells have many mitochondria, which provide the energy needed for the companion cells to load sugars from the mesophyll cells into the sieve tubes by active transport
holes in the sieve plates allow rapid flow of manufactured food substances through the sieve tubes

1. d) Absorbs light energy for photosynthesis.

Adaptation of photosynthetic cell: Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.

2. Typically the outer layer of bark will prevent sunlight from penetrating to within the trunk. Cells need sunlight to do photosynthesis. Light does not reach the cells in the trunk, and there’s no chlorophyll there.

B1.6 Diffusion AQA GCSE Biology B1 Cell Strucutre And Transport :Page No. 15

1. Diffusion. Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen. Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration.
2. a) An increase in temperature increases the speed at which molecules move at. An increased speed will yield faster and more even diffusion. A decrease in temperature will cause molecules to slow down. This will slow diffusion and make the spread of molecules less even.
3. b) So many cells have folded membranes along at least one surface because  as the particles on the outer cell wall are hot and melt the side and diffusion happens slower

Answer d Absorbs light energy for photosynthesis.

Adaptation of photosynthetic cell: Packed with chloroplasts. Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight.

2. Typically the outer layer of bark will prevent sunlight from penetrating to within the trunk. Cells need sunlight to do photosynthesis. Light does not reach the cells in the trunk, and there’s no chlorophyll there.

B1.7 Osmosis AQA GCSE Biology B1 Cell Strucutre And Transport :Page No. 17

1.A Diffusion is the movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. A good example of diffusion is food colouring.

It is the diffusion of a substance through a semipermeable membrane from a more dilute solution to a more concentrated solution. This process is also passive since no external energy is needed. Example: Absorption of water by plant roots.

B Plant cells have a strong rigid cell wall on the outside of the cell membrane. This stops the cell bursting when it absorbs water by osmosis. The increase in pressure makes the cell rigid. This is useful as plants do not have a skeleton. Instead the leaves and shoots can be supported by the pressure of water in their cells. If plant cells lose too much water by osmosis they become less rigid and eventually the cell membrane shrinks away from the cell wall.

The tendency of molecules of a solvent to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, equalizing the concentrations on each side of the membrane

2.a.i. Isotonic: a solution in which the solute and solvent are equally distributed–a cell normally wants to remain in an isotonic solution, where the concentration of the liquid inside of it equals the concentration of the liquid outside of it

(ii) Hypotonic: a solution which contains more solvent than solute (example: purified water–there’s almost no solute dissolved in the solvent (water) )

(iii) hypertonic: a solution which contains more solute than solvent (example: a lot of salt (solute) dissolved in water (solvent)

1. b) Because if the solute is too high, the cell will lose fluid through osmosis. If too low, the cell will gain fluid through the same process. Both can cause the cell to die.
2. Answer Osmosis takes place in an amoeba much like any other single-celled aquatic organism, with water diffusing across its cell membrane into the cell because of the higher concentration of solutes in its cytoplasm. Indeed, in many freshwater amoebas, this water movement is constant and at a high rate, enough to damage or even burst the cell if not regularly removed. Fortunately, amoebas have a sophisticated system to remove excess water.Amoeba has contractile vacuole Because of their constant intake of water via osmosis, water must actively be moved out of the cell with great frequency. Small, membrane-bound bubbles of pure water, collected from the cytoplasm, are brought to the contractile vacuole, which then contracts, pumping its contents back into the environment.

B1.8 Osmosis in plants AQA GCSE Biology B1 Cell Strucutre And Transport  :Page No. 19

1. a process by which molecules of a solvent tend to pass through a semi permeable membrane from a less concentrated solution into a more concentrated one

2 When you put the beetroot into a beaker of solution, water will move into or out of the tissue cells by osmosis. If the solution in the beaker is stronger than the solution in the cytoplasm, then the water will move out of the cells. This will make them shrink slightly and so overall the beetroot sample will shrink slightly. There is decrease in the size of beet root.

If the solution in the beaker is weaker than the solution in the beetroot cells then the water will move from the solution and into the cells. This will make them swell slightly and the sample get bigger. There is gain in the size of beetroot.

If the solution in the beaker is isotonic than there is no change in the size of the beet root.

As the concentration of water increased, the mass lost by the beetroot slowly decreased until it was actually gaining mass. This was because it had less water molecule than solution it was in. this was able to happen because the low level of water in the strong solution meant

that the net movement of water molecule was from the beetroot, through partially permeable membrane of the beetroot and into the solution.

The stronger the solution was, the more water had to move from the beetroot to the solution. As the strength of the solution decreased, less water had to move through the membrane from the beetroot. Eventually, the solution  was so weak that there was higher water con concentration in the solution than in the beetroot. This meant that the net movement of the water molecules was from the solution to the beetroot. This caused an increase in mass as I predicted.

3. Osmosis is important to plants. They gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them turgid or stiff so that they are able to hold the plant upright.

Osmosis ensures that all cells and structures within a plant have correct water pressure and volume.

Osmosis is a specific form of diffusion, the movement of molecules from areas of high concentration to areas of low concentration.

Osmosis is the diffusion of water molecules through semipermeable membranes. A cell membrane surrounds plant cells, just like animal cells. Plant cells also have an additional outer layer, the cell wall, that is much more rigid than the cell membrane. As water enters a plant cell it collects in fluid-containing organelles, or vacuoles.

Pressure inside the cell increases as vacuoles fill with water, lending rigidity to the cell wall and the entire plant. Plants that do not receive enough water wilt because there is not enough pressure in their cells to support the structure of the plant. Conversely, cells that fill with too much water begin to burst, causing brown spots on plant leaves.

Osmosis is the control by which cells maintain just the right amount of water. If the concentration of water molecules is higher outside of the cells, water flows into the plant’s cells. But, if the concentration is higher inside the cells, excess water flows out. Plants absorb water from the soil through osmosis in their root cells.

When water concentrations around a plant’s roots are higher than inside the plant, water flows into the roots and then, through continuing osmosis, up the stem into the rest of the plant. During photosynthesis osmotic pressure in the cells of plant leaves causes openings, or stomata, in the leaves to open.

Once open the stomata begin to absorb the carbon dioxide that is vital for photosynthesis to occur.

B1.9 Active Transport AQA GCSE Biology B1 Cell Strucutre And Transport : Page No. 21

1.Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient – and therefore require an input of energy from the cell.

Sometimes dissolved molecules are at a higher concentration inside the cell than outside, but, because the organism needs these molecules, they still have to be absorbed.

There are two types of active transport:

1) Primary Active Transport – Primary active transport, also called direct active transport, directly uses energy to transport molecules across a membrane. Most of the enzymes that perform this type of transport are transmembrane ATPases. A primary ATPase universal to all life is the sodium-potassium pump, which helps to maintain the cell potential. Other sources of energy for Primary active transport are redox energy and photon energy (light).

An example of primary active transport using Redox energy is the mitochondrial electron transport chain that uses the reduction energy of NADH to move protons across the inner mitochondrial membrane against their concentration gradient.

An example of primary active transport using light energy are the proteins involved in photosynthesis that use the energy of photons to create a proton gradient across the thylakoid membrane and also to create reduction power in the form of NADPH.

2) Secondary Active Transport – In secondary active transport or co-transport, energy is used to transport molecules across a membrane; however, in contrast to primary active transport, there is no direct coupling of ATP; instead, the electrochemical potential difference created by pumping ions out of the cell is used. The two main forms of this are antiport and symport.

2. a) Active transport requires energy ( ATP molecules ), while osmosis and diffusion require a concentration difference between the cell and its surrounding.

Diffusion is the movement of dissolved solutes or gases from an area of high concentration to an area of low concentration (down a concentration gradient). This is a passive process and so requires no energy in order to take place.

Osmosis is the movement of water down a concentration gradient) across a partially permeable membrane. Once again, this is a passive process and no energy is required.

Active transport is the movement of dissolved solutes across a membrane against a concentration gradient (moving from low to high concentration). This process requires a carrier protein, and energy in the form of ATP is required.

1. b) plants must exchange materials with their environment. These exchanges include absorbing water and minerals from the soil and absorbing carbon dioxide from the air for photosynthesis. Therefore plants have specialised exchange surfaces which maximise the efficiency of these exchanges.the roots is to absorb water from the soil by osmosis and dissolve mineral ions from the soil by active transport. the root hair cell contains lots of mitochondria.
2. a)

These marine creatures take in too much salt from the sea water that they drink and the kidneys can’t get rid of it.

Special salt glands are found near the eyes and nostrils, and sodium ions are moved here. These ions have to be moved against a very big concentration gradient, meaning active tranport is vital for the birds’  survival.

1. b) Active Transport in Plant Cells

Plants require mineral salts such as nitrates for growth. The concentration of nitrates is higher on plant root cell than it is in the soil solution surrounding it. The plant cannot rely on diffusion as the nitrates would diffuse out of root cell into the soil

B1.10 Exchanging Materials   AQA GCSE Biology B1 Cell Strucutre And Transport : Page No. 23

1. Two adaptation of an effective exchange surface are:

Having a large surface area over which exchange can take place

Having a thin membrane or being thin to provide a short diffusion path

2. Australian Fitzroy river turtle can breathe underwater. Inside the rear opening are two large sacs lined with finger like folds which provide a large surface area and rich blood supply for gas exchange. The muscular opening pumps water in and out, ventilation the fold and maintaining a steep concentration gradient for gas exchange.

But fish need to exchange oxygen and carbon dioxide between their blood and the water in which they swim. This happens across the gills, which are made up of stack of thin filament, each with a rich blood supply. Fish need a constant flow of water over their gills to maintain the concentration gradient needed for gas exchange. They get this by pumping water over the gills using a flap that covers the gills called operculum.

Summary questions: Page No. 25

1. Without microscopes we cannot see most cells.

Light microscopes

show cellular structure of living organisms and some subcellular structures (e.g., nucleus and chloroplasts) allow observation of living cells and staining of cells to show different features

Electron microscopes

enable examination of cells in great detail help determine what goes on within individual body cells can only be used for dead specimens in a vacuum

2. a) A: genetic material

B: cytoplasm

C: cell membrane

D: cell wall         E: plasmids                        F: flagella

1. b)

size range 10–100 μm

1. c) Similarities

cell walls

cell membrane

cytoplasm

differences

bacteria cells much smaller than plant cells

chloroplasts present in some plant cells

permanent vacuoles present in plant cells

slime capsules present in some bacteria cells

flagella present in some bacteria cells

genetic material contained in chromosomes in a nucleus in plant

cell, single DNA loop found free in the cytoplasm with additional

small loops of DNA known as plasmids in bacterial cell

1. d) bacteria are 1–2 orders of magnitude smaller than eukaryotic cells contain free genetic material can reproduce mitochondria and chloroplasts are similar in size to bacteria contain genetic material so they can reproduce independently of the cell dividing
2. a) similarities

Any one from:

random movement of particles

takes place down concentration gradient

Difference

only water moves in osmosis

1. b) Similarities

both are mechanisms for moving substances in and out of cells

Differences

only specific substances are moved by active transport

active transport takes place against concentration gradient

1. c) Water will move into both A and B by osmosis as inside of bag is hypertonic to outside.

Water will move into bag B faster than into bag A due to higher temperature.

Increased temperature gives increased rate of random particle movement.

Increasing the rate at which water particles would pass through the partially permeable membrane and speeding up osmosis.

1. d) i) useful model though effects of active transport are not demonstrated

(ii) shows what happens inside the cell but does not model effect of cell wall (very important in osmotic events in plant cells)

4. a)

Amoeba is single-celled organism with large surface area to volume ratio.

It is able to get sufficient oxygen through diffusion across the cell membrane.

Stickleback is larger, more complex multi-cellular organism with lower surface area to volume ratio.

Diffusion cannot provide sufficient oxygen for each cell, so a more effective exchange system (gills) is required.

1. b) Thin filament structure of gills greatly increases surface area available for exchanging gases.

Pushing water across gills increases rate of oxygen absorption by maintaining steep concentration gradient between water and blood.

Circulating blood delivers oxygen to cells.

Removes metabolic waste.

Maintaining steep concentration gradient at exchange surfaces in gills to increase diffusion further.

5.a) large surface area

thin membrane/being thin

efficient blood supply

1. b) Large surface area provides greater area over which exchange can take place (e.g., villi in small intestine, alveoli in lungs, plant root hair cells).

Thin membrane/being thin provides short diffusion path/increased efficiency

Efficient blood supply maintains steep concentration gradient Being ventilated maintains steep concentration gradient

Practice questions Page No. 27

1.1. cell membrane

1.2. cytoplasm

1.3. (animal cell does not have)

• cell wall
• chloroplast(s)
• (large) vacuole

2.1. 9 micrometres

2.2. 3.84 (mm)

2.3. (prokaryotic cells) are smaller do not have a nucleus

3.1. Osmosis

water moves from a dilute solution to a more concentrated solution through a partially / semi / selectively permeable membrane

3.2. cut potato cylinders to same mass / size

• use same volume of salt solution
• same temperature
• leave for same length of time
• dry cylinders before weighing
• put cylinders into a range of salt solution concentrations
• measure mass / size at start
• measure mass / size after a day or few days
• repeats
• observe whether the cylinders have increased / decreased or stayed the same mass / size
• correct description of direction of water movement
• conclusion: salt solution concentration in which cylinder did not change in mass / size is same concentration as in cells.

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  References:

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