Cell structures

Question 1

What characteristics must an organism display in order to be classified as living?

Answer 1

Movement
Respiration (or some mechanism of producing energy)
Sensitivity
Nutrition
Excretion
Reproduction
Growth

Question 2

What organelle can be seen clearly with a CLM?

Answer 2

The nucleus, chloroplast, vacuole… Other features that can be seen but are too small to be clearly defined are called granules.

Question 3

What is the ultrastructure of a chell?

Answer 3

Detailed structure of a cell containing features that can only be seen by a TEM.

Question 4

What is ‘Division of labour’?

Answer 4

Each organelle in a cell has a specific role and function, but working together to ensure the survival of the cell.

Question 5

What is the cytoskeleton?

Answer 5

A network of fibres made out of proteins.

Question 6

What is the role of the cytoskeleton?

Answer 6

1. To support the structure of the cell.
2. Actin filaments are able to move against each other, causing the cell to move. They also move around organelles inside the cell.
3. Microtubules are cylinders around 25nm in diameter. They can be involved in transporting chemicals around the cell or transporting organelles around the cell. This involves energy (from ATP) and is carried out by proteins on the microtubules called microtubule motors.

Question 7

Cell features that can be seen with CLM.

Answer 7

Nucleus
Chloroplast 
Mitochondria
Cytoplasm
Cell surface membrane
Golgi apparatus
Cell wall
Vacuole
Plasmodesma
Centriole
Ribosome
Tonoplast
Chromatin
Middle lamella
Grana

Question 8

Cell features that can be seen with TEM only (ultrastructure).

Answer 8

Microtubules
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Lysosome
Microvilli
Nuclear pores
Chloroplast envelope
Nuclear envelope
Secretory vesicles
Golgi vesicles

Question 9

Cell features only present in animal cells.

Answer 9

Centrioles
Pinocytotic vesicles*
Secretory vesicles*

Question 10

Cell features only present in plant cells.

Answer 10

Chloroplast
Cell wall
Plasmodesma
Tonoplast
Middle lamella
Grana
Chloroplast envelope*

Question 11

Cell features present in both cell types.

Answer 11

Nucleus
Mitochondria
Cytoplasm
Cell surface membrane
Golgi apparatus
Vacuole
Ribosome
Nuclear envelope
Chromatin
Microtubules*
Rough ER*
Smooth ER*
Lysosome*
Nuclear pores*
Golgi vesicles*

Question 12

What is the nucleus for?

Answer 12

Usually around 10-20 micrometers in diameter. Contains genetic material of cell. Controls the division and activity of the cell. The nuclear envelope consists of two membranes; the outer and inner membrane. It can be continuous with ERs and can be lined with ribosomes. Along the nuclear envelope are many nuclear pores 40-100nm wide that allow and regulates the exchange of chemicals between the nucleus and cytoplasm. The liquid inside the nucleus is known as nuclear sap or nucleoplasm.

Question 13

What’s inside the nucleus?

Answer 13

DNA is usually bound to proteins called histones and forms chromatin that coil to form chromosomes.
The chromatin on the edges of the nucleus are usually more coiled than the inside. They stain darker and are called heterochromatin whereas the rest on the inside are called euchromatin.
There is also one or more spherical structures called nucleoli. They are responsible for synthesising rRNA which is needed in ribosome formation.

Question 14

What are microvilli?

Answer 14

Finger-like projections off the surface of cells that increase cell surface area by up to x25. A surface lined with microvilli is called a brush border and they are usually found on cells specialised for excretion/ absorption, e.g. the illeum lining cells.

Question 15

What is the Rough Endoplasmic Reticulum for?

Answer 15

Consists of a network of flattened membrane sacs called cisternae. Ribosomes are bound onto the surface which is why it looks rough. The ER itself is involved in storage and transport of proteins.

Question 16

What is the Smooth Endoplasmic Reticulum for?

Answer 16

Involved in the synthesis, storage and transport of lipids.

Question 17

What is the structure of mitochondria?

Answer 17

A spherical or sausage-shaped organelle bound with two membranes separated by a fluid filled space; the outer membrane and the inner membrane which is folded into many cristae to increase surface area. The central part of the ribosome is called the matrix and contains a circular ring of DNA, ribosomes and phosphate granules.

Question 18

What is the function of mitochondria?

Answer 18

Site of aerobic respiration (using oxygen to produce energy).
Coupled mitochondria produce ATP which is involved in providing energy for most cellular activities.
Uncoupled mitochondria produce heat and is involved in keeping an organism warm.

Question 19

What is the Endosymbiont theory of mitochondrial origin?

Answer 19

A very long time ago, the mitochondria was actually a prokaryotic cell that aerobically respired and produced ATP but was one day engulfed by a eukaryotic cell as food. However, instead of digesting the mitochondria, a permenant symbiotic relationship was formed between the mitochondria and eukaryotic cell which involved the mitochondria providing the cell with energy and ATP while the cell provided the mitochondria with a stable environment and a steady supply of nutrients.

Question 20

What evidence is there to support the Endosymbiont theory of mitochondrial origin?

Answer 20

1. The mitochondria contains a circular ring of DNA, like a prokaryotic cell.
2. Mitochondria contains free-floating 70s ribosomes, like a prokaryotic cell.
3. Inner mitochondrial membrane is of similar composition to membrane of prokaryotic cell.
4. Affected by some antibiotics, like prokaryotic cells.

Question 21

What is the structure of ribosome?

Answer 21

Ribosomes are one of the few organelles not bound by its own membrane. There are two types of ribosomes; 70s ribosomes are small and are found in prokaryotic cells, mitochondria and chloroplasts. 80s ribosomes bigger are found in eukaryotic cells.
Ribosomes are made out of rRNA and proteins, forming a large and small subunit. In eukaryotic cells, they can be found either floating freely or bound to rough ER.

Question 22

What is the function ribosome for?

Answer 22

Ribosomes are responsible for protein synthesis. They read the instructions of making proteins carried by mRNA molecules and they assemble amino acids to form the required proteins.

Question 23

What is the structure of chloroplast?

Answer 23

Found is plant cells and some protocists. The chloroplast is bound by an envelope consisting of an outer membrane and an inner membrane. The fluid bound by these membranes is called the stroma. The stroma contains flattened membranes called thycaloid which contain the pigment chlorophyll and is where photosynthesis occurs. The chloroplast also contains starch grains (product of photosynthesis) lipid droplets, circular ring of DNA and ribosomes.

Question 24

What is the function of chloroplast?

Answer 24

Site of photosynthesis. Where light energy is used to convert carbon dioxide and water into glucose and oxygen.

Question 25

What is the Endosymbiont theory of chloroplast origin?

Answer 25

Similar to mitochondria.

Question 26

What evidence is there to support the Endosymbiont theory of chloroplast origin?

Answer 26

1. The chloroplast contains a circular ring of DNA, like a prokaryotic cell.
2. Chloroplast contains free-floating 70s ribosomes, like a prokaryotic cell.
3. Inner chloroplast membrane is of similar composition to membrane of prokaryotic cell.
4. Affected by some antibiotics, like prokaryotic cells.

Question 27

What is the structure of Golgi apparatus?

Answer 27

Layers of flattened membranes (cisternae) stacked on top of each other. There are two sides of the Golgi; the forming side where the lipid and protein vesicles are fusing and the maturing side where the Golgi vesicles are diffusing back into the cytoplasm.

Question 28

What is the function of the Golgi apparatus?

Answer 28

The Golgi is involved in the modifying and packaging of chemicals. For example; lipids and proteins into lipoproteins or carbohydrates and proteins into glycoproteins. It then packages them into small, membrane bound vesicles ready for excretion from the cell.

Question 29

`What is the structure of a lysosome?

Answer 29

A membrane bound vesicle containing digestive chemicals and acid to maintain an optimum pH.

Question 30

What is the function of lysosome?

Answer 30

To break down materials inside or outside of the cell. E.g. a white blood cell.

Question 31

What are membranes for?

Answer 31

1. To separate the cytoplasm from the outside contents.
2. To separate organelles from the cytoplasm.
3. To control the movement of chemicals in and out of the cell.
4. Where chemicals that contribute towards self recognition are held. Preventing autoimmunity and helping with development of organism.
5. Houses many receptors essential for the sensitivity of the cell.
6. Site of some chemical reactions. Enzymes may attach to the surface membrane.

Question 32

What is the basic chemical structure of a membrane?

Answer 32

The main structure of any membrane consists of mainly phospholipid molecules. These molecules consist of hydrophilic phosphate heads bonded to hydrophobic lipid tails. Charge is evenly distributed within the molecule so the phospholipid doesn’t dissolve in water easily. When it’s surrounded by water, phospholipids form a bilayer where two layers of hydrophilic phosphate groups sandwich hydrophobic lipid tails between them. There are usually other components to a membrane as well, like glycolipids, cholesterol and other proteins.

Question 33

What is the fluid mosaic model of membranes?

Answer 33

This is currently the widely accepted model for describing the structure of membranes. This model states that the main structure of a membrane is composed of a phospholipid bilayer with other chemicals like proteins, cholesterol etc. embedded into it.
The fluid part refers to how the phospholipid molecules in the bilayer aren’t held together by any bonds so they and all other components in the membrane are free to move about the bilayer plain,
The mosaic part refers to all the proteins and other chemicals embedded into the phospholipid bilayer, like a mosaic.