Cells

Give one similarity in the way in which active transport and facilitated diffusion transport substances across the membrane

Involves transport proteins

Organelles labelled X all have very similar shapes in this cell. Explain why they appear to have different shapes in this drawing.

Sections cut at different angles/in different planes

Some liver tissue was ground, filtered and centrifuged to make a suspension of mitochondria. Explain why the solution in which the liver tissue was ground should be ice-cold.

Slows enzymes/prevents enzymes being denatured

Give one way in which active transport differs from facilitated diffusion

Requires energy

One function of a surface protein

1. Cell recognition 2. Binding to hormones

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue

1. Break open cells and remover debris 2. First pellet added is nucleus 3. Solution is cold/buffered to stop enzyme reactions from happening and to balance the PH 4. Second pellet added is chloroplast

Name two structures that are present in plant cells but not present in animal cells

1. Cell wall 2. Chloroplast

Describe two functions of hydrophobic tails

1. Form impermeable barrier to water-soluble substances 2. Allows non-polar molecules to pass through 3. Allows cell to maintain different concentrations either side

This photograph was taken using a transmission electron microscope. The structure of the organelles visible in the photograph could not have been seen using an optical(light) microscope. Explain why.

1. Has low resolution 2. Because wavelength of light is too long

The scientists used a transmission electron microscope to study the structure of the amoeba. Explain why.

1. Higher resolution 2. Shorter wavelength 3. To see internal structures

Describe how phospholipids are arranged in a plasma membrane.

1. In a bilayer 2. Hydrophobic/fatty acid tail to inside 3. Polar hydrophilic head to outside

Function of chloroplasts

1. Photosynthesis 2. Uses light 3. To produce carbohydrates/starch/glucose etc.

If Villi are damaged why do people have low concentrations of amino acids in their blood?

1. Reduced surface area so less absorption 2. Membrane-bound enzymes less effective so protein/polypeptides not digested

There are a large number of mitochondria in a cell. Explain how these organelles help the cell absorb the products of digestion.

1. Site of aerobic respiration 2. Convert glucose into energy in form of ATP 3. ATP energy used to move digestion products against a concentration gradient 4. Through process of active transport

Mitochondria is found in large numbers in cells which take up substances by active transport. Explain why

1. Site of aerobic respiration which releases energy 2. required for movement against concentration gradient

Chlamydomonas lives in fresh water ponds. Use your knowledge of osmosis to suggest an advantage of using starch as a carbohydrate store.

1. Starch is insoluble 2. Reduces water entry - osmotically inactive

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure. Explain the advantages and the limitations of using a TEM to investigate cell structure

Advantages: Small objects can be seen TEM has high resolution as wavelength of electrons is shorter Limitations: Cannot look at living cells as cells must be in a vacuum Preparation may create artefact Does not produce colour image

Organelle X is a mitochondrion. What is the function of this organelle?

Aerobic respiration

Large numbers of mitochondria and Golgi apparatus are found in mucus-secreting cells. Explain why.

Golgi - modifies/packages/adds sugars to proteins Mitochondria - Provides ATP for this

Name two structures in a eukaryotic cell that cannot be identified using an optical microscope

Lysosomes Ribosomes Mitochondrion ER

Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus

Mitochondria - Site of aerobic respiration, releasing energy in the form of ATP

Name two structures that show a eukaryotic cell.

Nucleus Mitochondrion Endoplasmic reticulum Lysosome

The ground liver was centrifuged at low speed. the pellet that formed at the bottom of the tube was thrown away and the supernatant centrifuged again at higher speed. Explain why it was necessary to first centrifuge the ground liver at low speed in order to obtain a suspension of mitochondria.

To remove the nuclei, which are larger/more dense

Cells that secrete enzymes contain a lot of RER and a large Golgi apparatus. i) Describe how the RER is involved in the production of enzymes ii) Describe how the Golgi apparatus is involved in the secretion of enzymes

i) RER has ribosomes to make proteins. Amino acids are joined together ii) Golgi modifies proteins and packages them into secretory vesicles

The flowchart shows how chloroplasts may be obtained from leaves In the first step in this procedure, the leaves were homogenised by grinding in cold buffer solution. Explain why. i) the leaves were homogenised ii) a buffer solution was used

i) break open cells/release cell contents ii) keep PH the same