Module 2: section 1- Cell structure

Question 1

what are the organelles in an animal cell?

Answer 1

-plasma (cell surface) membrane
-rough endoplasmic reticulum
-nucleolus
-nucleus
-smooth endoplasmic reticulum
-lysosome
-ribosome
-nuclear envelope
-golgi apparatus
-cytoplasm
-mitochondrion

Question 2

what are the organelles in a plant cell?

Answer 2

plasma (cell surface) membrane
-CHLOROPLAST
-rough endoplasmic reticulum
-PLASMODESMA
-mitochondrion
-golgi apparatus
-VACUOLE
-smooth endoplasmic reticulum
-cytoplasm
-nuclear envelope
-nucleolus
-nucleus
-ribosome
-CELL WALL

Question 3

what is the plasma membrane and the composition&function

Answer 3

Term: Plasma (cell surface) membrane
Description: The membrane found on the surface of animal cells and inside the cell wall of plant cells and prokaryotic cells.
Composition: Made of lipids and proteins.
Function: Regulates the movement of substances in and out of the cell, and contains receptor molecules to respond to chemicals like hormones.

Question 4

what is a cell wall and its composition&function

Answer 4

Term: Cell wall
Description: A rigid structure that surrounds plant cells.
Composition: Made of the carbohydrate cellulose.
Function: Supports plant cells.

Question 5

what is the nucleus and its function?

Answer 5

Term: Nucleus
Description: A large organelle surrounded by a nuclear envelope with pores, containing chromatin (DNA and proteins) and a nucleolus.
Function: Controls the cell’s activities by regulating DNA transcription. The nucleolus makes ribosomes.

Question 6

what is the lysosome and its function?

Answer 6

Term: Lysosome
Description: A round organelle surrounded by a membrane, with no clear internal structure.
Function: Contains digestive enzymes to break down invading cells or worn-out cell components.

Question 7

what is the ribosome and its function&composition

Answer 7

Term: Ribosome
Description: A very small organelle that can either float free in the cytoplasm or be attached to the rough endoplasmic reticulum.
Composition: Made of proteins and RNA.
Function: The site where proteins are made.

Question 8

what is the rough endoplasmic reticulum and its function?

Answer 8

Term: Rough Endoplasmic Reticulum (RER)
Description: A system of folded membranes called cisternae enclosing a fluid-filled space. The surface is covered with ribosomes.
Function: Folds and processes proteins made at the ribosomes. synthesising proteins that need to leave the cell.

Question 9

what is the smooth endoplasmic reticulum and its function?

Answer 9

Term: Smooth Endoplasmic Reticulum (SER)
Description: Similar to the rough endoplasmic reticulum, but with no ribosomes.
Function: Synthesises and processes lipids. and stores lipids and carbohydrates.

Question 10

what is the vesicle and its function

Answer 10

Term: Vesicle
Description: A small fluid-filled sac in the cytoplasm, surrounded by a membrane.
Function: Transports substances in and out of the cell (via the plasma membrane) and between organelles.

Question 11

what is the golgi apparatus and its function?

Answer 11

Term: Golgi Apparatus
Description: A group of fluid-filled, folded membrane-bound, flattened sacs, making cisternae. Vesicles are often seen at the edges.
Function: Processes and packages new lipids and proteins; also makes lysosomes. add carbohydrates to proteins to form glycoproteins, produce secretory enzymes, secrete carbohydrates, transport, modify and store lipids, molecules are “labelled” with their destination, vesticles pinch off the cisternae which transports molecules out of the cell

Question 12

what is the mitochondrion and its function?

Answer 12

Term: Mitochondrion
Description: Usually oval-shaped with a double membrane. The inner membrane is folded to form cristae, and inside is the matrix, which contains enzymes involved in respiration.
Function: The site of aerobic respiration, where ATP is produced. Found in active cells requiring lots of energy.

Question 13

what is the chloroplast and its function?

Answer 13

Term: Chloroplast
Description: A small, flattened structure in plant cells, surrounded by a double membrane. Contains thylakoid membranes stacked into grana, linked by lamellae, and surrounded by stroma.
Function: The site of photosynthesis. Some parts happen in the grana, and other parts in the stroma.

Question 14

what is the centriole and its function?

Answer 14

Term: Centriole
Description: Small, hollow cylinders made of microtubules (tiny protein cylinders). occur in pairs to form a centrosome. Found in animal cells and only some plant cells.
Function: involved in the production of spindle fibres. Involved in the separation of chromosomes during cell division.

Question 15

what is cilia and its function?

Answer 15

Term: Cilia
Description: Small, hair-like structures on the surface membrane of some animal cells. In cross-section, they have an outer membrane and a ring of nine pairs of protein microtubules, with two microtubules in the middle. (Known as 9+2 formation)
Function: The microtubules allow the cilia to move. This movement is used to move substances along the cell surface.

Question 16

what is flagellum and its function?

Answer 16

Term: Flagellum
Description: Flagella on eukaryotic cells are like cilia but longer. They stick out from the cell surface and are surrounded by the plasma membrane. They contain two central microtubules and nine pairs around the edge.
Function: The microtubules contract to move the flagellum, propelling the cell forward (e.g., in sperm cells).

Question 17

how does protein production work in a cell?

Answer 17

-proteins are made in the ribosomes
-the ribosomes on the rough endoplasmic reticulum make the proteins that are excreted or attached to the cell membrane. the free ribosomes in the cytoplasm make proteins that stay in the cytoplasm. new proteins produce at the rough endoplasmic reticulum are folded and processed in the rough ER. then theyre transported from the ER to the golgi apparatus in vesicles. at the golgi apparatus, the proteins may undergo further processing. the proteins enter more vesicles to be transported around the cell.

Question 18

What are the main steps involved in the production and secretion of proteins in a cell?

Answer 18

1. Synthesis: Polypeptide chains are synthesized on the rough endoplasmic reticulum (RER) by ribosomes.
2. Transport to Golgi: Polypeptide chains move to the cisternae in the RER, are packaged into vesicles, and are transported to the Golgi apparatus via the cytoskeleton.
3. Modification and Packaging: In the Golgi apparatus, proteins are modified and packaged into vesicles.
4. Secretion: Secretory vesicles carry proteins to the cell surface membrane, where they are released by exocytosis.

Question 19

what are the several functions of the cytoskeleton?

Answer 19

the cytoskeleton has 4 main functions:
-the microtubules and microfilaments support the cells organelles keeping them in position.
-they also help to strengthen the cell and maintain its shape.
- theyre responsible for the movement of materials within its cell. e.g the movement of chromosomes when they separate during cell division.
-the proteins in the cytoskeleton can also cause the cells to move. e.g the movement of cillia or flagella is caused by the cytoskeletal protein filaments that run through them. cytoskeleton propels the whole cell.

Question 20

what are the comparisons between eukaryotic cells and prokaryotic cells?

Answer 20

• Size: Prokaryotes are smaller (< 2 µm), while eukaryotes are larger (10-100 µm).
  
  • DNA Structure: Prokaryotes have circular DNA free in the cytoplasm; eukaryotes have linear DNA enclosed in a nucleus.
  • Nucleus: Prokaryotes lack a nucleus; eukaryotes have a nucleus.
  • Cell Wall: Prokaryotes have a polysaccharide cell wall (peptidoglycan); eukaryotes have cellulose (plants) or chitin (fungi) cell walls, none in animals.
  • Organelles: Prokaryotes lack membrane-bound organelles; eukaryotes have them (e.g., mitochondria).
  • Flagella: Prokaryotic flagella are made of flagellin in a helix; eukaryotic flagella have a “9+2” microtubule arrangement.
  • Ribosomes: Prokaryotes have smaller ribosomes; eukaryotes have larger ribosomes.
  • Examples: E. coli (prokaryote), Human liver cell (eukaryote).

Question 21

organelles in prokaryotic cells (bacteria)

Answer 21

-flagellum
-DNA (bacterial chromosome)
-plasma (cell surface) membrane
-ribosome
-cell wall
-plasmid (ring of DNA)
1. plasmids are roughly 10th the size of eukaryotic cells
2. this means that normal microscopes arent really that powerful enough to look at their internal structure
3. can be seen under an electron microscope

Question 22

What is magnification in microscopy?

Answer 22

Magnification is how much bigger the image appears compared to the actual size of the object.

Question 23

What is resolution in microscopy, and why is it important?

Answer 23

Resolution is the ability to distinguish between two points that are close together. Higher resolution provides clearer and more detailed images.

Question 24

How do you calculate the magnification of an image?

Answer 24

The formula for magnification:
magnification= image size/object size

Units for magnification are typically written as “X” (e.g., 100X means 100 times magnification).

Question 25

Name the main types of microscopes discussed.

Answer 25

1. Light Microscopes
2. Electron Microscopes (Transmission electron microscope and scanning electron microscope)

Question 26

What are the characteristics of light microscopes?

Answer 26

Light microscopes are common and use light to visualize specimens.
• They have a maximum magnification of about 1,500X.
• Their maximum resolution is around 0.2 micrometers (µm).

Question 27

Why might light microscopes be limited in observing cells?

Answer 27

Light microscopes are limited by their resolution, which means they may not clearly show smaller cell structures due to the wavelength of light.

Question 28

What is the difference between TEM and SEM?

Answer 28

Transmission Electron Microscopes (TEM) beam of electrons pass through the specimen (species are extremely thin and stained, placed in a vacuum). some parts of the specimen absorb the electrons and this makes them appear darker. the image produced is detailed, high-resolution 2D images of the internal structure.
* Scanning Electron Microscopes (SEM) specimen does not need to be thin as the electrons are not transmitting through. electrons are beamed across the specimen onto the surface. this knocks off electrons from the specimen which are gathered in a cathode ray tube to form an image. this produces a 3D image of the surface of the specimen.

Question 29

Why do electron microscopes have higher resolution than light microscopes?

Answer 29

Electron microscopes use electrons instead of light, which have shorter wavelengths. This allows them to achieve a higher resolution, distinguishing much smaller structures within cells. the image is created using an electromagnet to focus the beam of negatively charged electrons.

Question 30

What are the typical magnification and resolution capabilities of TEM and SEM?

Answer 30

TEM: Maximum magnification of around 1,000,000X with a resolution of 0.0002 µm.
• SEM: Maximum magnification of around 500,000X with a resolution of 0.002 µm.

Question 31

why do electron microscopes have a higher resolution and why cant living specimens be used?

Answer 31

a beam of electrons has a very short wavelength so it has a high resolution, smaller structures can be visualised
the image is created using an electromagnet to focus the beam of negatively charged electrons. living samples cant be used as the air would absorb the electrons so specimens must be in a vacuum. the image is also black and white so stain must be used.

Question 32

Why is staining important in microscopy?

Answer 32

Staining is crucial because in light microscopes, images are produced by passing light through the object being observed. Some components may appear transparent, making it difficult to distinguish different parts. Staining adds colour to various components, making them more visible and easier to study.

Question 33

How does staining work for light microscopes?

Answer 33

Different stains bind to specific parts of the cell or sample. For example:
• Eosin stains the cytoplasm.
• Methylene blue stains DNA.
This specificity helps differentiate between cellular structures, enhancing visibility.

Question 34

What stains are used for electron microscopes, and why?

Answer 34

In electron microscopy, objects are usually dipped in solutions of heavy metals like lead. The metal ions scatter the electrons, creating contrast. Areas where the metal accumulates appear darker, aiding in differentiating structures.

Question 35

How do you prepare a dry mount microscope slide?

Answer 35

Place the Specimen on the Slide: Use a thin slice of the specimen so light can pass through. Place it directly on a clean glass slide.
2. Add the Cover Slip: Carefully lower a cover slip over the specimen at a 45-degree angle to avoid trapping air bubbles.

Question 36

How do you prepare a wet mount microscope slide?

Answer 36

Add Water or Stain: Place a drop of water or stain on a clean slide.
2. Place the Specimen: Put the specimen into the drop for better visibility.
3. Add the Cover Slip: Lower the cover slip at a 45-degree angle to reduce air bubbles.
4. Remove Excess Liquid: Use filter paper at the cover slip’s edge to absorb any extra liquid.

Question 37

How do you use a light microscope to view a specimen?

Answer 37

Clip the slide onto the stage.
2. Use the lowest-powered objective lens first.
3. Adjust the coarse adjustment knob to move the stage up to just below the lens, then slowly bring it down until the specimen is in focus.
4. Adjust the focus with the fine adjustment knob and switch to higher magnification if needed, re-focusing as necessary.

Question 38

What is an eyepiece graticule and how is it used?

Answer 38

An eyepiece graticule is a transparent ruler in the microscope’s eyepiece with a scale (usually 100 divisions) for measuring specimen size. It has no specific units until calibrated with a stage micrometer.

Question 39

What is a stage micrometer and how is it used to calibrate the eyepiece graticule?

Answer 39

A stage micrometer is a slide with a precise scale, often 1 mm in length with 0.01 mm (10 µm) divisions. To calibrate, align the graticule with the stage micrometer to calculate the real measurement each division represents at a given magnification.

Question 40

How do you calculate the size of a specimen using a calibrated eyepiece graticule?

Answer 40

Measure the specimen length in graticule units. Multiply by the value of each unit as determined by calibration. This gives the real length in micrometres.

Question 41

What common issues can arise when preparing slides for exams?

Answer 41

Students often forget the basic steps: correctly staining the sample, calibrating measurements with the graticule and micrometer, and preparing the slide without air bubbles, all of which can affect accuracy.