1.2: Ultrastructure of Cells

Question 1

1.2.U1 Outline the major differences between prokaryote and eukaryote cells

Answer 1

Prokaryote__Eukaryote

Tiny (0.2-2um) Bigger (10-100um)

Nucleoid (no nuclear membrane) True nucleus

No organelles Organelles present

Flagella rotates Flagella moves laterally

Cell wall of peptidoglycan Cell wall of cellulose (plants) or chitin (fungi)

Smaller 70s ribosomes Larger 80s ribosomes

DNA is circular, naked DNA is linear, with histones

Has plasmids Does not have plasmids

Asexual cell division Asexual or sexual reproduction

Question 2

1.2.U1 Describe the function in a prokaryotic cell of the cell membrane

Answer 2

Responsible for regulating what materials move into and out of the cell.

Question 3

1.2.U1 Describe the function in a prokaryotic cell of the nucleoid

Answer 3

The genetic material (DNA)

Circular, naked DNA

Question 4

1.2.U1 Describe the function in a prokaryotic cell of plasmids

Answer 4

Genetic material often with genes for antibiotic resistance

Question 5

1.2.U1 Describe the function in a prokaryotic cell of cytoplasm

Answer 5

Gel-like fluid substance, site of many metabolic reactions

Question 6

1.2.U1 Describe the function in a prokaryotic cell of ribosomes

Answer 6

Build proteins during translation

Question 7

1.2.U1 Describe the function in a prokaryotic cell of the cell wall

Answer 7

Outer peptidoglycan covering that protects and provides shape to the cell

Question 8

1.2.U1 Describe the function in a prokaryotic cell of pili

Answer 8

Hair-like structures that help the cell attach to surfaces

Question 9

1.2.U1 Describe the function in a prokaryotic cell of the capsule

Answer 9

Helps maintain moisture and adhere to surfaces. Protects cell from other organisms.

Question 10

1.2.U1 Describe the function in a prokaryotic cell of a flagella

Answer 10

Long extensions used in locomotion

Question 11

1.2.U1 Define extracellular

Answer 11

“Extra cellular” means outside the cell. Any structure outside the cell membrane is considered extracellular:

• cell wall
• pili
• capsule
• flagella

Question 12

1.2.U1 Contrast the size of eukaryote and prokaryote ribosomes

Answer 12

Prokaryotes have smaller, 70s ribosomes. Eukaryotes have larger, 80s ribosomes. The s stands for Svedberg units (a measure of particle sedimentation rate).

Question 13

1.2.U2 State the meaning and advantage of eukaryotic cells being “compartmentalised”.

Answer 13

Compartmentalization: the presence of membrane bound partitions (aka. organelles) inside the eukaryotic cell. These compartments allow for:

1. Specialization for specific functions without interference from other cell functions. For example, lysosomes can digest cell debris without digesting the cell itself.
2. Allows molecules needed for a function (for example enzymes or ions) to reach a higher concentration than if all molecules were diluted in the cytoplasm. For example, the mitochondria accumulate a large H+ concentration which is used to fuel ATP synthesis.

Question 14

1.2.A2 Define asexual reproduction

Answer 14

Asexual reproduction creates offspring from a single organism. The offspring are genetic clones of that parent.

Question 15

1.2.A2 Outline the four steps of binary fission

Answer 15

1. The (nucleoid) DNA replicates to create an exact genetic copy
2. The (new nucleoid) DNA attaches to the cell membrane close to the original
3. The cell membrane (and wall, if present) grow, causing the cell to elongate and the DNA molecules to move apart from each other
4. The The cell membrane (and wall, if present) pinch inwards, creating two genetically identical cells.

Question 16

1.2.U4 Define resolution

Answer 16

Resolution is the shortest distance between two points that can be distinguished as separate.

Question 17

1.2.U4 Compare the maximum resolution of a light microscope with that of an electron microscope

Answer 17

Light microscopes can resolve to about 200nm apart. Electron microscopes can resolve to about 0.2nm apart (1000x better than light).

Question 18

1.2.U4 List 3 example structures that are visible with electron microscopes but not with a light microscope.

Answer 18

Electron microscopes have stronger magnification and better resolution and therefore can produce images with better detail. For example the ribosomes, Golgi, ER and cytoskeleton are not visible with a light microscope but can be seen with the electron microscope.

Question 19

1.2.A1 State the function of an exocrine gland cell

Answer 19

Exocrine gland cells synthesize molecules (often protein enzymes) for secretion from the cell into an external space (for example, a salivary gland)

Question 20

1.2.A1 Describe the function of the following structures in an exocrine gland cell

Answer 20

Plasma (cell) membrane: regulates passage of materials into and out of the cell.

Nucleus: contains the genetic code (used to make proteins) and contains the nucleolus (where ribosomes are synthesized).

Mitochondria: location of cellular respiration used to make ATP. The ATP can then be used to fuel the cells protein synthesis, transport and secretion processes.

Golgi apparatus: modifies proteins before they are used, stored or released from the cell.

Lysosome: contains digestive enzymes that can be used to break apart cellular debris and waste.

Vesicles: transport materials within the cell and out of the cell via exocytosis

Endoplasmic reticulum: ribosomes on the rough ER synthesis proteins which are then moved through the ER and packaged into vesicles for transport.

Question 21

1.2.A2 State the function of a palisade mesophyll cell

Answer 21

Palisade mesophyll cells are found on the upper surface of a leaf and have the primary job of performing photosynthesis.

Question 22

1.2.A2 Describe the function of the following structures in a palisade mesophyll cell

Answer 22

Cell wall: provides structural rigidity and support

Plasma (cell) membrane: regulating passage of materials into and out of the cell

Chloroplast: location of photosynthesis

Vacuole: water filled sac that helps maintain cell turgidity

Nucleus: holds DNA, the genetic code for making proteins. Also has the nucleolus, where ribosomes are synthesized

Mitochondria: site of cellular respiration, where glucose chemical energy is converted to ATP chemical energy

***plant cells have other organelles as well, like ER, vesicles and Golgi

Question 23

1.2.S1 Explain why the ultrastructure of prokaryotic cells must be based on electron micrographs

Answer 23

Ultrastructures are small structures of/in a biological specimen that sre too little to see with a light microscope

Question 24

1.2.S1 Draw the ultrastructure of E. coli

Answer 24

Question 25

1.2.S2 Recognise features and identify structures in micrographs of eukaryotic cells.

Given a micrograph, draw and label the ultrastructure of a eukaryotic cell.

Answer 25

Question 26

1.2.S3 Explain why cells with different functions will have different structures

Answer 26

Cells have different organelles depending on the primary function of the cell type. This allows cells to specialise for a specific task which can lead to increased complexity of the entire organism.

Question 27

1.2.S3 Identify ultrastructures visible in a micrograph of a eukaryotic cell

Answer 27

Typically visible ultrastructures are:

• nucleus - look for nuclear membrane and the nucleolus
• rough ER - look for long sheets of membrane with little black dots attached (typically close to the nucleus)
• cell membrane - look ofr a thin line around the edge of the cell
• Golgi - look for stacks of membrane, typically further from nucleus
• lysosome - little, clear sacs. Hard to distinguish from vesicles
• mitochondria - often stain dark; look for internal lines
• ribosomes - look like little, dark dots. Can be “free” in the cytoplasm or bound to the rough endoplasmic reticulum
• vesicles - look for smaller clear circles
• chloroplast - typically an oval shape with stacks seen on the inside
• vacuole - looks like a vesicle, but is typically larger in size
• cell wall - thicker, clear line outside of the cell membrane

Question 28

1.2.S3 Given a micrograph of a cell, deduce the function of the cell based on the structures present

Answer 28

Cells will have specialised shapes given their function. For example:

small intestine villus cell - microvilli increase surface area for absorption; many mitochondria for fueling active transport

hormone secreting cell - many vesicles holding the hormones until secretion

photosynthetic plant cell - chloroplasts for performing photosynthesis

Question 29

1.2.NOS1 With reference to a specific example, explain how an improvement in apparatus allowed for greater understanding of cell structure

Answer 29

The invention of the electron microscope in 1931 led to better resolution when viewing cells. For example, mitochondrial structure was discovered.