Cell specialisation

Question 1

What is a zygote?

Answer 1

A fertilized egg cell; the first stem cell. Divides by mitosis without increasing in size.

Question 2

What is a morula?

Answer 2

A solid ball of ~16 cells formed ~3 days after fertilization.

Question 3

What is a blastocyst?

Answer 3

Formed when morula reaches ~64 cells; has a fluid-filled cavity and an inner cell mass (stem cells).

Question 4

What are stem cells?

Answer 4

Differentiate into many types of cells

Self-renew to maintain the stem cell pool

Create functional tissue by replacing damaged or dead cells

Question 5

What drives stem cell differentiation?

Answer 5

Signaling factors like morphogens—they activate or silence genes using transcription factors.

Question 6

Do all cells have the same genes?

Answer 6

Yes. Differentiation depends on which genes are switched on/off, not on gene presence.

Question 7

Totipotent

Answer 7

Can form any cell type including placenta (e.g., zygote).

Question 8

Pluripotent

Answer 8

Can form most cell types in the body (e.g., inner cell mass of blastocyst).

Question 9

Multipotent

Answer 9

Can form a few closely related cell types (e.g., adult stem cells in bone marrow).

Question 10

Unipotent

Answer 10

Can only form one specific cell type (e.g., liver stem cells).

Question 11

What is a stem cell niche?

Answer 11

A location in the body that keeps adult stem cells undifferentiated until needed.

Question 12

Hematopoietic stem cells

Answer 12

Found in bone marrow → make blood cells (RBCs, WBCs, platelets).
Used in bone marrow transplants (e.g., leukemia treatment).

Question 13

Hair follicle stem cells

Answer 13

Involved in hair growth, skin innervation, wound healing.
Possible uses: skin grafts, hair regrowth.

Question 14

What are meristems?

Answer 14

Regions of unspecialised cells in plants capable of division.

Question 15

Types of meristems:

Answer 15

Apical meristems (tips of roots/shoots) → height/length

Lateral meristems (between xylem/phloem) → width/thickness (growth rings)

Question 16

Why does cell size matter?

Answer 16

Exchange = surface area

Metabolism = volume

As cells grow, SA:Vol ↓ → inefficient exchange → cell must divide.

Question 17

Adaptations to increase SA:Vol:

Answer 17

Villi & microvilli (intestine)

Biconcave shape (RBCs)

Extended shape (nephron tubules)

Question 18

Sperm Cell Adaptations:

Answer 18

Haploid nucleus for fertilization

Cortical granules prevent polyspermy

Surrounded by:

Zona pellucida: sperm binding, triggers acrosome reaction

Follicle cells: from secondary follicle

Question 19

Muscle Cell Types:

Answer 19

Skeletal muscle: long, tubular, unbranched → 1D contraction

Cardiac muscle: branched, contacts multiple cells → faster signal spread

Smooth muscle: slow, involuntary movements (e.g., digestive tract)

Question 20

What are gametes?

Answer 20

Gametes are cells formed by meiosis that have a haploid nucleus. They carry genetic information from parents to offspring. Males produce sperm, and females produce eggs.

Question 21

Adaptations of sperm cells

Answer 21

Haploid nucleus for fusion with egg’s nucleus

Acrosome contains enzymes to penetrate the egg

Tail for motility

Mitochondria to power movement

Question 22

Adaptations of egg cells

Answer 22

Large size with yolk-rich cytoplasm (nutrients for embryo)

Haploid nucleus paused in metaphase II (meiosis completes after fertilization)

Mitochondria to power cell division (sperm don’t contribute mitochondria)

Question 23

What are cortical granules?

Answer 23

Vesicles in egg’s cytoplasm that release enzymes after fertilization to make the zona pellucida impenetrable to other sperm (preventing polyspermy).

Question 24

What is the zona pellucida?

Answer 24

A layer of glycoproteins surrounding the egg. It binds sperm and initiates the acrosome reaction. It’s chemically changed after fertilization to prevent polyspermy.

Question 25

What is the corona radiata?

Answer 25

A layer of follicle (granulosa) cells around the egg that provide protection and nutrients. They remain around the egg after ovulation.

Question 26

What are binding proteins on the egg cell?

Answer 26

Proteins on the egg’s plasma membrane that bind to proteins on the sperm’s acrosome membrane during fertilization.

Question 27

What is the yolk in an egg cell?

Answer 27

Cytoplasm filled with nutrients for early development. Makes egg much larger than sperm (about 10,000 times larger).

Question 28

Red blood cell adaptations

Answer 28

Small and flexible to pass through capillaries Bi-concave shape increases surface area for oxygen exchange No nucleus, allowing more space for hemoglobin

Question 29

B-lymphocyte adaptations (white blood cells)

Answer 29

Small when inactive Increase in size during infection to make antibodies Have more rough ER and Golgi when active

Question 30

What do B-lymphocytes do?

Answer 30

Produce and secrete antibodies that inactivate pathogens.

Question 31

Cerebellar granule cell adaptations

Answer 31

Very small neurons in the cerebellum Small size allows brain to pack ~50 billion for sensory-motor integration

Question 32

Motor neuron adaptations

Answer 32

Large cell body with many organelles for making proteins and neurotransmitters Very long axon (up to 1 meter) to send signals from spine to muscles/glands

Question 33

What do motor neurons do?

Answer 33

Transmit signals from the central nervous system to muscles and glands.