Cell Structure–Seneca

Question 1

Similarities of Prokaryotic and Eukaryotic Cells

Answer 1

• Both contain organelles.
• The cell-surface membrane made of phospholipid bilayer–responsible for controlling the passage of substances across exchange surfaces.

Question 2

Prokaryotes

Answer 2

Prokaryotes are simple, single-celled organisms.

Question 3

Eukaryotes

Answer 3

Eukaryotes are complex, multicellular organisms.

Question 4

Differences of Prokaryotic and Eukaryotic Cells

Answer 4

• Prokaryotic cells–single-celled prokaryotic organisms.
• Eukaryotic cells make up complex eukaryotic organisms.
• Eukaryotic cells are larger and more complex than prokaryotic cells.
• Cells arise from other cells by:
- binary fission in prokaryotic cells
- mitosis or meiosis in eukaryotic cells.

Question 5

Animal Cell

Answer 5

Contains: 
– Mitochondria.
– Ribosomes.
– Endoplasmic reticulum (ER).
– Golgi.
– Lysosomes.
– Nucleus.
– Animal cells are enclosed by a cell membrane.

Question 6

Plant Cell

Answer 6

Contains: 
– Mitochondria.
– Ribosomes.
– Endoplasmic reticulum (ER).
– Golgi.
– Lysosomes.
– Nucleus.
– Plant cells also possess:
– Vacuole (a repository of cell sap).
– Chloroplasts (the site of photosynthesis).
– Cell wall (made of cellulose and contains plasmodesmata, through which cells exchange substances with each other).

Question 7

Algal Cells

Answer 7

Contains: 
– Mitochondria.
– Ribosomes.
– Endoplasmic reticulum (ER).
– Golgi.
– Lysosomes.
– Nucleus.
– Vacuole (a repository of cell sap).
– Chloroplasts (the site of photosynthesis).
– Cell wall (made of cellulose and contains plasmodesmata, through which cells exchange substances with each other).

Question 8

Fungal cells

Answer 8

Contains: 
– Mitochondria.
– Ribosomes.
– Endoplasmic reticulum (ER).
– Golgi.
– Lysosomes.
– Nucleus.
– Vacuole (a repository of cell sap).
– Cell wall (made from chitin)

Question 9

Cell Specialisation

Answer 9

A cell specialises because the shape and contents of a cell help it to carry out its function.

Examples include:
• Muscle cells–active–contain lots of mitochondria–produce ATP.

Question 10

Cell Organisation

Answer 10

• Specialised cells are organised into tissues to organs to organ systems.

Question 11

Structure and Function of Plasma Membrane

Answer 11

Structure
• Made from a phospholipid bilayer.
• Have proteins and cholesterol embedded in them.
• Proteins can act as receptors–cell can respond to the external environment of the cell.

Function
• Controls the passage of organic molecules, ions, water, and oxygen into and out of the cell.
• Waste products leave the cell by passing through the plasma membrane.

Question 12

Structure and Function of Cytoplasm

Answer 12

Structure
• Made up of organelles suspended in the gel-like cytosol.
• 70% made up of water.
• Also contains proteins, sugars, ions and fatty acids.

Functions
• Many metabolic reactions take place.
• Different organelles perform specific functions.

Question 13

Nucleus

Answer 13

A big organelle that contains the cell’s DNA. It is surrounded by a nuclear envelope.

Question 14

Structure and Function of Nuclear Envelope

Answer 14

Structure
• The double-membrane structure that has a number of pores.
• Both the inner and outer membranes are phospholipid bilayers.

Function
• The pores control the passage of ions, molecules and RNA between the nucleoplasm and cytoplasm.

Question 15

Structure and Function of Nucleus

Answer 15

Structure
• The nucleoplasm is the semi-solid fluid inside the nucleus, where we find the chromatin and the nucleolus.
• In eukaryotes, the nucleus contains linear chromosomes that are made up of DNA.
• There is an area within the nucleus called the nucleolus (plural = nucleoli).

Function
• Controls the actions of the cell.
• DNA contains instructions for the synthesis of proteins.
• Ribosomal RNA is joined together with associated proteins in the nucleolus to assemble the ribosomal subunits.

Question 16

Mitochondria

Answer 16

Mitochondria produce adenosine triphosphate (ATP) via aerobic respiration.

Question 17

Structure and Function of Mitochondria

Answer 17

Structure
• Oval-shaped, double-membrane organelles that have their own ribosomes and DNA.
• Each membrane is a phospholipid bilayer embedded with proteins.
• The inner layer of the membrane has folds called cristae.
• The area surrounded by the folds is called the mitochondrial matrix–contains enzymes used for respiration.

Function
• Mitochondria make ATP via aerobic respiration.
• Muscle cells–high concentration of mitochondria–highly active–need energy–keep body moving.

Question 18

Structure and Function of Chloroplasts

Answer 18

Structure
• Have own DNA, ribosomes and have inner and outer membranes.
• The space enclosed by the inner membrane contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids.
• Each stack is called a granum (plural = grana).
• Grana are linked by lamellae.
• Lamellae are flat, thin parts of thylakoid membrane.
• The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.

Function
• Photosynthesis happens in chloroplasts and allows plants to make their own food.
• Found in plant and algal cells but not in animal cells.

Question 19

Chloroplasts

Answer 19

Chloroplasts are plant cell organelles that carry out photosynthesis.

Question 20

Structure and Function of the Golgi Apparatus

Answer 20

Structure
• Series of flattened membranous sacs.

Function
• Transport vesicles form from the endoplasmic reticulum and fuse with the Golgi apparatus.
• Empty proteins and lipids into the lumen of the Golgi apparatus.
• As the proteins and lipids travel through the Golgi, they are sorted, packaged and tagged to be sent to the right place.

Question 21

Structure and Function of the Golgi Vesicles

Answer 21

Structure
• Membrane-bound, fluid-filled vesicles.
• Small, round and are seen in a high density near the edges of the sacs.
• Lysosomes are a type of Golgi vesicle.

Function
• Golgi vesicles store and transport modified proteins and lipids.
• Lysosomes are a special type of Golgi vesicle. They contain enzymes called lysozymes.
• Lysozymes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids and old organelles.

Question 22

The Functioning of the Golgi Apparatus (steps)

Answer 22

1. Transport vesicles from the ER and fuse with the Golgi apparatus
   
   2. Empty their contents into the lumen of the Golgi apparatus
   3. As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted
   4. Newly modified proteins and lipids are packaged into secretory vesicles that bud from the Golgi

Question 23

Ribosomes and the Endoplasmic Reticulum

Answer 23

Proteins are made in ribosomes. Proteins may then be folded and processed by the RER. The SER makes and processes lipids.

Question 24

Structure and Function of Ribosomes

Answer 24

Structure
• Ribosomes can be free floating in the cytoplasm or attached to the cytoplasmic side of the endoplasmic reticulum (ER).
• Ribosomes are very small organelles made of protein subunits. This means that ribosomes are NOT covered by a membrane.

Function
•Protein synthesis.
• Protein synthesis is an essential function of all cells. Found in practically every cell.

Question 25

Structure and Function of Endoplasmic Reticulum

Answer 25

Structure
• Series of interconnected membranous sacs and tubules.
• The membrane of the ER is a phospholipid bilayer embedded with proteins.
• The SER membrane has no ribosomes but the RER membrane has many ribosomes on its surface.

Function
• The RER is responsible for processing and folding proteins.
• The SER is responsible for making and processing lipids.

Question 26

Cell Wall

Answer 26

The cell wall is a structure external to the plasma membrane.

Question 27

Structure and Function of Cell Walls

Answer 27

Structure
• The cell wall is a rigid covering that protects the cell.
• Plant, fungal and algal cells all have cell walls.
• Cellulose is a polysaccharide made up of glucose units.

Function
• Provides structural support and gives shape to the cell.

Question 28

Structure and Function of Cell Vacuoles

Answer 28

Structure
• Occupies most of the area of the cell.
• These vacuoles are surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap.
• Cell vacuoles are found in the cytoplasm of plant cells but are NOT present in animal cells.

Function
• Allows the cell to remain rigid.
• Holds more water, the vacuole pushes against the cell wall and pressure is maintained. Stops the plant from wilting.

Question 29

Cell Vacuole

Answer 29

Cell vacuoles are found in plant cell cytoplasm.

Question 30

DNA in prokaryotes

Answer 30

• Found in a circular molecule.
• Some have smaller loops of DNA called plasmids.
• Bacteria can exchange plasmids with other bacteria, sometimes receiving beneficial new genes.
• Antibiotic resistance often spreads through a bacterial colony through plasmid exchange.

Question 31

Prokaryotes vs Eukaryotes

Answer 31

Features common to these types of cells are:
• A plasma membrane.
• Cytoplasm.
• DNA.
• Ribosomes (ribosomes are smaller in prokaryotes).

Main difference in terms of organelles is that prokaryotes do NOT have any membrane-bound organelles.

Question 32

Ribosome Productions

Answer 32

• Ribsomnal RNA joins with proteins–form ribsomnal subunits
• Subunits formed in the nucleolus
• Exit via the pores in the nuclear envelope

Question 33

Cell Fractionation

Answer 33

Cell fractionation separates organelles according to size to allow them to be studied in an electron microscope.

Question 34

Steps of Cell Fractionation

Answer 34

1) Homogenisation
• Sample is homogenised using a blender to break the cells.

2) Filtration
• Sample is filtered into tubes through a gauze.
• Gauze separates larger components from the smaller organelles.
• Filtered into tubes to be fractionated using ultracentrifugation.

3) Ultracentrifugation
• Spun at a low speed in a centrifuge.
• Each tube must be balanced with another tube directly opposite for the centrifuge to work properly.
• Separates the sample into fractions.
• Heavier organelles are forced to the bottom of the tube.
• Lighter organelles move towards the top.
• Cell debris forms a pellet at the bottom of the tube, leaving the supernatant above it that contains the organelles.
• The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles (the nuclei).
• This is repeated at increasingly higher speeds to separate each fraction.

4) Order of fractionation
• The process of repeated ultracentrifugation produces factions of cell organelles from heaviest to lightest.

Question 35

Organelles in the order of heaviest to lightest

Answer 35

• Nucleus.
• Chloroplasts.
• Endoplasmic reticulum.
• Mitochondria.
• Lysosomes.
• Ribosomes.

Question 36

In what conditions should the tissue sample be kept in (for cell fractionation)?

Answer 36

• Ice cold (reduces enzyme activity that might damage organelles).
  
  • Isotonic solution (prevents osmosis that could shrink or burst organelles).
  • No osmosis takes place in isotonic solution.
  • Buffered solution (avoids damaging the protein structures).