Eukaryote organelles

Question 1

Nucleus

Answer 1

• nuclear membrane is double and has pores through it
• nucleus contains the chromosomes, consisting of DNA associated with histone proteins
• where DNA is replicated and transcribed to form rNA, which is exported via the nuclear pores to the cytoplasm
• uncoiled chromosomes are spread through the nucleus and are called chromatin
• there are often densely staining areas of chromatin around the edge of the nucleus

Question 2

Rough endoplasmic reticulum (rER)

Answer 2

• consists of flattened membrane sacs called cisternae
• attached to the outside of these cisternae are ribosomes (they are larger than in prokaryotes and are classified as 80S)
• main function of rER: synthesise protein for the secretion from the cell - protein synthesized by the ribosomes of the rER passes into its cisternae and is then carried by vesicles, which bud off and are moved to the Golgi apparatus

Question 3

Golgi apparatus

Answer 3

• consists of flattened membrane sacs called cisternae, like rER
• however the cisternae aren’t as long, are often curved, don’t have attached ribosomes and have many vesicles nearby
• function: processes proteins brought in vesicles from the rER; most of these proteins are then carries in vesicles to the plasma membrane for secretion

Question 4

Lysosomes

Answer 4

• approximately spherical with a single membrane
• formed from Golgi vesicles
• contain high concentrations of protein, which makes them densely staining in electron micrographs
• contain digestive enzymes, which can be used to break down ingested food in vesicles or break down organelles in the cell or even the whole cell

Question 5

Mitochondrion

Answer 5

• double membrane surrounds mitochondria, with the inner part folded to form structures called cristae
• fluid inside is called the matrix
• shape of mitochondria variable but usually spherical or ovoid
• produce ATP (energy) for the call by aerobic cell respiration
• fat is digested here if it is being used as an energy source in the cell

Question 6

Free ribosomes

Answer 6

• appear as dark granules in the cytoplasm and are not surrounded by a membrane (also 80S as with rER)
• synthesize protein, releasing it to work in the cytoplasm, as enzymes or in other ways
• ribosomes are constructed in a region of the nucleus called the nucleolus

Question 7

Chloroplast

Answer 7

• double membrane surrounds the chloroplast
• inside are stacks of thylakoids, which are flattened sacs of membrane
• produce glucose and a wide variety of other organic compounds by photosynthesis
• starch grains may be present inside the chloroplasts if they have been photosynthesizing rapidly

Question 8

Vacuoles and vesicles

Answer 8

• these are organelles that consist simply of a single membrane with fluid inside
• many plant cells have large vacuoles that occupy more than half of the cell volume
• some animals absorb foods from outside and digest them inside vacuoles
• some unicellular organisms use vacuoles to expel excess water
• vesicles are very small vacuoles used to transport materials inside the cell

Question 9

Microtubules and centrioles

Answer 9

• in the cytplasm of cells there are small cylindrical fibres called microtubules that have a variety of roles, including moving chromosomes during cell division
• animal cells have structure called centrioles, which consist of two groups of nine triple microtubules
• centrioles form an anchor point for microtubules during cell division and also for microtubules inside cilia and flagella

Question 10

Cilia and flagella

Answer 10

• contain a ring of nine double microtubules plus two central ones
• can be used for locomotion
• cilia can also be used to create a current in the fluid next to the cell