Stem cells in animals and plants

What type of stem cells are found in bone marrow?

• Bone marrow contains adult stem cells

• These stem cells are multipotent

• They can differentiate into several types of blood cell

Give examples of differentiated cells produced from bone marrow stem cells.

• Erythrocytes (red blood cells)

• Neutrophils (white blood cells)

What is the function of erythrocytes?

• Transport oxygen around the body

• Oxygen is carried by haemoglobin

Why must new erythrocytes be produced continuously?

• Mature erythrocytes lack a nucleus

• They cannot undergo mitosis

• New erythrocytes are formed from bone marrow stem cells

What nuclear change occurs as erythrocytes differentiate?

• Loss of the nucleus

• Creates more space for haemoglobin

• Improves oxygen transport efficiency

How does erythrocyte shape change during differentiation?

• Develop a biconcave disc shape

• Increases surface area to volume ratio

• Shortens diffusion distance for oxygen

What other changes occur as erythrocytes differentiate?

• Increased production of haemoglobin

• Increased membrane flexibility

• Allows cells to pass through narrow capillaries

What is the function of neutrophils?

• Destroy pathogens by phagocytosis

• Part of the non-specific immune response

How does the nucleus change in neutrophils?

• Nucleus becomes lobed

• Allows greater flexibility

• Enables movement through capillary walls

How do neutrophils adapt to digest pathogens?

• Increased production of hydrolytic enzymes

• Enzymes break down pathogens after phagocytosis

What happens to lysosomes in neutrophils?

• Large numbers of lysosomes accumulate

• Lysosomes contain hydrolytic enzymes

• Essential for pathogen digestion

Why does membrane flexibility increase in neutrophils?

• Allows neutrophils to change shape

• Helps them move into tissues to reach pathogens

Where are stem cells found in plants?

• In regions of active growth

• These regions are called meristems

What tissues arise from plant stem cells?

• Xylem

• Phloem

What is the cambium?

• A type of lateral meristem

• Found between xylem and phloem

• Produces new xylem and phloem cells

What is the function of xylem tissue?

• Transport water and mineral ions

• Provide structural support

Why is lignin deposited in xylem cell walls?

• Strengthens the walls

• Prevents collapse under tension

• Provides mechanical support

What happens to the contents of xylem cells during differentiation?

• Loss of cytoplasm

• Cells become dead

• Allows unimpeded water flow

Why are end walls lost in xylem vessels?

• Forms continuous tubes

• Enables efficient upward water transport

What is the function of phloem tissue?

• Transport assimilates (e.g. sucrose and amino acids)

• Transport occurs by translocation

How does cytoplasm change in phloem sieve tube elements?

• Reduced cytoplasm volume

• Creates space for mass flow of sap

What happens to organelles in sieve tube elements?

• Loss of some organelles

• Reduces resistance to flow

• Cells remain living

What are sieve plates and why are they important?

• Perforated end walls between sieve tube elements

• Allow assimilates to flow between cells