B2.3: Cell specialisation

2025 New syllabus

What are the adaptations of cardiac muscle cells and striated muscle fibres

Muscle tissues exerts pulling forces as it contracts.

Striated muscles: attached to the skeleton. contraction --> exerts force on bone to maintain or change posture. (I.E. locomotion or for ventilation).

Muscles have: enclosed plasma membrane but many nuclei.

Both cardiac muscle and skeletal striated muscles have:

• Contractile myofibrils.

• Large amount of mitochondria --> supplies the ATP for contraction.

Outline the - Adaptations of sperm and egg cells

Eggs cell and sperm - Adaptations: 

Mall gametes: 

• Motile (both plants and animals).

• produced in high number: increase chances of fertilisation. 

• Tail - swims fast to fertilise eggs.

• Small

• Contains acrosome enzymes to digest Zona pellucida.

Female gametes: 

• • Big: nutritents and food reserves: for possible embryo development. 

• acrosome reaction mechanism: allows only one sperm to penetrate;

• • Zona pellucida: tough and hard protecting the egg; restrict sperm entry. (Crotical genules hardens the Zona pellucida)

both are: Haploid cells (23n) 

How do cells become differentiated?

Differentiation is the process during development whereby newly formed cells become more specialised and distinct from one another as they mature.

• All cells share an identical genome – each cell contains the entire set of genetic instructions for that organism

• The activation of different instructions (genes) within a given cell by chemical signals will cause it to differentiate into different cell types

Why is the SA:V ratio different in each organism?

• The exhange of materials from the external environment is needed for chemical reactions in organisms. (differs in different organimsm).

• The rate of metabolism of a cell is a function of its Mass:V (larger cells need more energy to sustain essential functions)

• The rate of material exchange is a function of its SA:V (large membrane surface equates to more material movement)

As a cell grows, volume (units³) increases faster than surface area (units²), leading to a decreased SA:Vol ratio

• If metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:Vol ratio), the cell will eventually die

• Hence ,growing cells tend to divide and remain small in order to maintain a high SA:Vol ratio suitable for survival.

Cell size in specialisation

The size of cells can vary significantly in multicellular organisms in order to optimise the specific function of a cell

• RBCs need to squeeze through narrow capillaries and have a diameter of only 7–8 µm

• Neurons need to transmit signals throughout the body and can be over 1m in length (but with a width of only ~10 µm) 

• Striated muscle fibres consist of fused muscle cells – they can have a width of 20–100 µm and a length of up to 12 cm

• A human ovum (female egg) is one of the largest cells with a diameter of 120 µm, while the male sperm is extremely small (~5 µm)

Link: Cell Size and Scale

Totipotent

Can form any cell type, including embryonic cells, and develop into entirely new organisms

• embryonic stem cells

Pluripotent

– Can form any cell type arising from the three germ layers

• embryonic stem cells

Multipotent

Can only form a number of closely related cell types

• Adult stem cells.

Location and function of stem cell niches in adult humans

Stem cell niches are sites within the body where a pool of adult stem cells are maintained in preparation for future proliferation and differentiation

• Locations of stem cell niches in the human body include the bone marrow, hair follicles, heart, intestines and brain

Bone Marrow

• Haemopoietic stem cells are located within the bone marrow and give rise to the different types of blood cells (e.g. erythrocytes, leucocytes and thrombocytes)

• Bone marrow transplants are commonly employed to replace the haemopoietic stem cell niche following chemotherapy for leukemia (blood cell cancer)

Hair Follicles

• contain a range of epidermal stem cells that are involved in cyclic bouts of hair growth, skin innervation, vascularisation and wound repair

• These stem cells could potentially be harvested and used to regenerate skin tissue in burns victims (or stimulated to promote hair regrowth in bald individuals)