biology: organelles

Question 1

What is an organelle?

Answer 1

• subcellular structure
• one or more specific jobs to perform in the cell

Question 2

Describe the nuclues:

Answer 2

• bound by a double membrane (the nuclear envelope)
• envelope is not continuous - contains pores so substances can move between the nucleus and cytoplasm
• contains chromatin, in dividing cell, chromatin is tightly coiled to form chromosomes
• DNA controls protein synthesis, by producing mRNA during transcription - thus development and function of a cell

Question 3

Describe nucleolus:

Answer 3

• dense, spherical structure within the nucleus, responsible for the manufacture of ribosomal RNA, the subunits which form ribosomes (assembled in the cytoplasm)

Question 4

Describe mitochondria: part 1

Answer 4

• involved in aerobic respiration yielding ATP
• bound by two membranes, a smooth outer and highly folded inner membrane
• between outer and inner folded is the inter-membrane spcae
• folds of the inner membrane are called cristae, provide larger surface area for reactions of aerobic respiration

Question 5

Describe mitochondria: part 2

Answer 5

• is a fluid filled central part called the matrix, contains enzymes to catalyse reactions involved in respiration
• contains DNA and ribosomes
• cristae also contains membrane bound proteins, form electron transport chains
• involved in synthesis of ATP, along with enzyme ATP synthase
• contain 70S ribosomes in their matrix

Question 6

Describe the endoplasmic reticulum:

Answer 6

• consists of flattened membrane bound sacs
• surface has ribosomes, allows them to produce secretary proteins
• folding of proteins occur here

Question 7

Describe centrioles:

Answer 7

• at base of flagella and cilia
• absent in higher plants
• organises microtubules, which forms cells skeletal system
• help determine location of nucleus
• key role in cell division

Question 8

Describe plant cell wall:

Answer 8

• made up of cellulose
• thin layer in middle, called lamella, marks boundary between adjacent cell walls and cements them together
• protect and support the cell
• withstand turgor pressure (pressure from being full of water) to stop cell bursting

Question 9

Describe large permanent vacuole:

Answer 9

• fluid filled sac bounded by a single membrane
• single membrane around it is called tonoplast
• contains solution of mineral salts, sugar, waste
• helps maintain turgidity of plant
• acts as food store

Question 10

Describe chloroplasts: part 1

Answer 10

• filled with a fluid (stroma), where light reactions take place
• contain flattened sacs (thylakoids)
• liquid stroma contains 70S ribosomes and many enzymes to catalyse huge number of reactions)
• contains circular DNA

Question 11

What do thylakoid membranes contain and how are they arranged?

Answer 11

• contain pigment chlorophyll, absorbs light
• contains membrane proteins, form electron transport chains
• include enzyme ATP synthesis
• arranged in stacks called granum, increases surface area, maximise light absorbed

Question 12

What is the role and function of tonoplasts?

Answer 12

• partially permeable membrane of vacuole
• contains proteins that transport salts and solutes
• maintain turgor pressure

Question 13

What is the role of the plasmodesmata?

Answer 13

• microscopic channels
• travers cell walls of plant cells enable transport and communication
• extension of cytoplasm

Question 14

What are pits?

Answer 14

• holes that allow movement of water from one vessel to another if there s a blockage
• in plants, water is carried in xylem tissue
• series of tubes called xylem vessels
• modified deal cells