cell organelles

Question 1

Nucleus

Answer 1

• It’s a large organelle surrounded by nuclear envelope.
• Contains coded genetic information in the form of DNA.
• The nuclear envelope has nuclear pores that allow molecules to move into or out of the nucleus.
• Chromatin ,made up of DNA, is a complex formed from proteins called histones.
• A dense spherical structure known as the nucleolus is responsible for the production of ribosomes.

Question 2

Mitochondria

Answer 2

• The site of aerobic respiration where the molecule ATP(energy carrier) is produced.
• It’s double membraned:
  .the inner membrane is highly folded to form the structures called cristae.
  .the fluid interior is called the matrix
• It has a small amount of DNA.

Question 3

Vesicle

Answer 3

• Membranous sacs that have storage and transport roles.

Question 4

Lysosome

Answer 4

• A specialised form of vesicles that contain hydrolytic enzymes (breaking down).
• They break down waste materials and old organelles.

Question 5

Plasma membrane.

Answer 5

• It’s selectively permeable and controls the movement of substances into and out of the cell.
• It has receptor molecules that allow it to respond to chemicals like hormones.

Question 6

Cytoskeleton.

Answer 6

• A network of fibres made of protein.
  -Main functions: . support the organelles in the cell ; holding them in place.
  . transporting organelles and materials around the cell.
  . movement of chromatids during mitosis.
• Components:
  1- Microfilaments: formed from the protein actin and are responsible for cell movement.
  2- Microtubules: form a scaffold-like structure that determines the shape and act as tracks for the movement of the cell organelles.
  3- Intermediate fibres : these fibres give mechanical strength to cells and help maintain their integrity.

Question 7

Centrioles

Answer 7

• A component of cytoskeleton.
• They are composed of microtubules which are small hollow cylinders containing a ring of centrioles.
• Involved in the assembly and organisation of spindle fibres during cell division.

Question 8

Flagella

Answer 8

• They are whip-like structures that are longer than cilia.
• They have a 9 + 2 arrangement (however not in bacteria as they normally have a 9+0)

Question 9

Cilia

Answer 9

• Hair-like structures , made up of microtubules .
• They have a 9 + 2 arrangement ; pairs of parallel microtubules slide over each other causing the cilia to move in a beating motion.

Question 10

Ribosomes

Answer 10

• Very small organelles
• They are a site of protein synthesis.
• They are found in the cytoplasm and rough ER.

Question 11

Endoplasmic reticulum

Answer 11

• A network of membranes enclosing flattened sacs called cisternae .
• Connected to the outer membrane of the nucleus.
  The different types:
  1- Smooth ER : responsible for lipid and carbohydrate synthesis and storage.
  2- Rough ER : ribosome bound and responsible for the synthesis and transport of protein.

Question 12

Golgi apparatus

Answer 12

• A compact structure of cisternae.
• It further modifies proteins and lipids secreted by the ER.
• It packages them into vesicles which are pinched off and moved to extremities of the cell and bind with the membrane before release.

Question 13

Cellulose cell wall

Answer 13

• It’s freely permeable.
• It gives the plant cell shape.
• A structure called plasmodesmata , which are holes for exchanging substances with adjacent cells.

Question 14

Large permanent vacuole.

Answer 14

• Membrane lined sac containing cell sap.
• It’s important for the maintenance of turgor as it pushes the cytoplasm against the cell wall keeping the cell turgid.
• Its membrane is called tonoplast .

Question 15

Chloroplast

Answer 15

• A site of photosynthesis
• A double membrane structure
• The fluid enclosed in the chloroplast is called the stroma.
• They have an internal network of membranes that form flattened sacs called thylakoids ( several of them are called granum which are joined by membranes called lamelle.

Question 16

Describe how organelles work together to produce a protein.

Answer 16

• DNA is found in the nucleus. The instructions on the DNA are copied into a molecule called mRNA. The mRNA leaves the nucleus via nuclear pores and moves to a ribosome.
• The ribosome synthesises the protein.
• The protein is modified and moved through the rER attached to the ribosome and is pinched off into a transport vesicle.
• The vesicle then moves/travels and fuses with the golgi apparatus.
• At the golgi apparatus , the protein is further modified and processed and finally packaged as it’s pinched off into a secretory vesicle.
• This vesicle then moves towards the plasma membrane.
• The vesicle fuses with the plasma membrane and is secreted outside of the cell.