B2.3 Cell specialisation

What is fertilization?

Fertilization is the fusion of a male and female gamete to produce a single cell.

What happens to the single cell formed by fertilization in multicellular organisms?

It divides repeatedly to generate an embryo of many cells.

What process ensures that the cells in an embryo are genetically identical?

Mitosis ensures that the cells in an embryo are genetically identical.

What does the genome of embryonic cells allow them to do?

It allows them to develop in any way.

What is differentiation?

It is the development of cells in different ways to carry out specific functions.

Why is differentiation important for cells?

It allows cells to perform their functions more efficiently by developing ideal structures and specific enzymes.

How many distinct types of specialized cells are there in humans?

There are 220 distinct types of specialized cells in humans.

What does gene expression mean?

Gene expression means that a gene is switched on and used to produce a protein or other gene product.

Why does cell differentiation occur?

Cell differentiation occurs because different sequences of genes are expressed in different cell types.

What determines how a cell differentiates in an embryo?

A cell’s position in the embryo determines how it differentiates, guided by gradients of signaling chemicals.

What role does retinoic acid play in differentiation?

Retinoic acid guides differentiation in the development of organs like forelimbs, pancreas, lungs, and kidneys.

What is a stem cell?

A stem cell is an undifferentiated or partially differentiated cell capable of dividing repeatedly and differentiating into various cell types.

What is the stem cell niche?

It is the precise location in a tissue that provides the microenvironment for stem cells to remain inactive or differentiate as needed.

What happens to stem cells in striated muscle when injury occurs?

They proliferate and differentiate to replace damaged muscle tissue.

What do bone marrow and hair follicle niches promote?

They promote continuous stem cell proliferation and differentiation for blood cell production and hair growth.

What are totipotent stem cells?

Totipotent stem cells can differentiate into any cell type.

What are pluripotent stem cells?

Pluripotent stem cells can differentiate into many cell types but not all.

What are multipotent stem cells?

Multipotent stem cells can differentiate into several types of mature cells but are more restricted than totipotent or pluripotent cells.

What is an example of multipotent stem cells?

Haematopoietic stem cells in bone marrow are multipotent because they can generate different types of blood cells.

What is the primary function of sperm cells?

To transfer a haploid nucleus to the egg cell for fertilization.

How long is a human sperm cell?

A human sperm cell is approximately 50 µm long.

What is the primary function of egg cells?

To provide food reserves and structures necessary for embryo development.

How large is a human egg cell?

A human egg cell is approximately 110 µm in diameter.

What is the zona pellucida in an egg cell?

It is a layer of glycoproteins that binds sperm and prevents additional sperm from entering after fertilization.

What are cortical granules in an egg cell?

They are vesicles containing enzymes that make the zona pellucida impenetrable after sperm entry.

What do the mitochondria in egg cells do?

They produce ATP and divide to generate mitochondria for the adult body.

What is the role of the tail in a sperm cell?

The tail, or flagellum, generates the force needed for forward motion.

What is the function of the acrosome in a sperm cell?

It contains enzymes that digest the zona pellucida to allow sperm to reach the egg.

How do red blood cells’ shape and size support their function?

Their biconcave shape and small size increase surface area-to-volume ratio for faster oxygen exchange.

What is the approximate diameter of red blood cells?

Red blood cells are about 6–8 µm in diameter.

What is the purpose of microvilli in proximal convoluted tubule cells?

Microvilli increase surface area for reabsorbing useful substances from the filtrate.

What is the function of Type I pneumocytes in alveoli?

Type I pneumocytes are adapted for oxygen and carbon dioxide diffusion.

What is the role of Type II pneumocytes in alveoli?

Type II pneumocytes produce surfactant, which reduces surface tension and prevents alveolar collapse.

What are myofibrils in striated muscle fibers?

Myofibrils are cylindrical structures within muscle fibers responsible for contraction.

What is the role of intercalated discs in cardiac muscle?

Intercalated discs connect cardiac cells and allow rapid propagation of electrical signals.

What is the surface area-to-volume ratio?

It is the ratio of surface area to volume, critical for efficient substance exchange in cells.

What happens if a cell’s surface area-to-volume ratio is too small?

Substances enter slowly, waste accumulates, and the cell may overheat due to rapid metabolism.

What are the adaptations of alveoli for gas exchange?

Alveoli have a large surface area, thin walls, and a short diffusion distance.

What are B-lymphocytes?

B-lymphocytes are white blood cells that enlarge to become plasma cells when activated.

How do proximal convoluted tubule cells selectively reabsorb substances?

Channel and pump proteins in the apical and basal membranes ensure only required substances are reabsorbed.

Why do motor neurons have a large cell body?

The large size allows enough protein synthesis to maintain their long axons.

What is the approximate length of a motor neuron axon?

It can extend for a meter or more.

What is the Z-line in myofibrils?

It is a disc-shaped structure in the center of each light band in myofibrils.

What is the main function of striated muscle fibers?

To exert force and contract for movement.

How are cardiac muscle cells different from skeletal muscle cells?

Cardiac muscle cells are shorter, branched, and connected by intercalated discs.

What is the role of the nucleus in egg cells?

The nucleus contains genetic material to be combined with the sperm nucleus during fertilization.

What is surfactant?

Surfactant is a phospholipid-protein layer in alveoli that reduces surface tension and prevents collapse.

How do sperm swim rapidly?

Sperm use their tail (flagellum) and ATP generated by mitochondria.

What is the approximate thickness of Type I pneumocytes?

They are about 0.15 µm thick.

Why do cerebellar granule cells have a very small cell body?

To allow the cerebellum to accommodate 50 billion of them.

What is the metabolic rate of a cell proportional to?

The metabolic rate is proportional to the cell's volume.

What is the significance of the haploid nucleus in gametes?

It ensures the correct chromosome number is restored after fertilization.

Why do muscle fibers have multiple nuclei?

They form by the fusion of embryonic muscle cells.

What is the primary role of mitochondria in sperm cells?

To supply ATP for tail movement.

Why do red blood cells lack mitochondria?

To maximize space for hemoglobin and oxygen transport.

How do gradients of signaling chemicals influence differentiation?

They determine a cell’s position in the embryo and its pathway of differentiation.

What is the primary function of white blood cells?

To defend the body by producing antibodies and other immune responses.

Why do striated muscle fibers have a striped appearance?

Myofibrils with alternating light and dark bands create the striped appearance.

What is the function of lamellar bodies in Type II pneumocytes?

They store and secrete phospholipids for surfactant production.

Why do muscle fibers contract?

To exert force and cause movement.

What is the primary function of the Golgi apparatus in plasma cells?

To synthesize and secrete proteins, such as antibodies.

What is the function of binding proteins in sperm cells?

They help the sperm bind to and penetrate the egg cell.

Why do egg cells have cortical granules?

To prevent additional sperm from penetrating after fertilization.

What is the purpose of centrioles in egg cells?

Centrioles are needed for mitosis.

How do skeletal muscles return to their original length after contraction?

Antagonistic muscles exert pulling forces to lengthen them.

Why are motor neurons essential for movement?

They carry signals from the central nervous system to distant muscles.

What is a key feature of alveolar epithelium?

It is one cell thick to facilitate gas exchange.

What is the main advantage of a high surface area-to-volume ratio in cells?

It allows for rapid exchange of substances.

What is the zona pellucida’s role in fertilization?

It prevents polyspermy by becoming impenetrable after one sperm enters.

How do sperm cells minimize resistance to movement?

They have a streamlined, narrow head and tightly packed nucleus.

What is the primary function of the yolk in egg cells?

To provide food reserves for the developing embryo.

What do proximal convoluted tubules reabsorb?

They reabsorb glucose, ions, and other useful substances.

What does the acrosome contain?

It contains enzymes that digest the zona pellucida of the egg.

Why are Type II pneumocytes larger than Type I pneumocytes?

They produce surfactant and have more organelles for synthesis.

Why is the surface area of alveoli important?

A large surface area increases the efficiency of gas exchange.

What is the process of fertilization? Fertilization is the fusion of a male and female gamete to produce a single cell, which divides repeatedly to form an embryo.

What is the function of mitosis in early embryo development? Mitosis ensures that the cells in the embryo are genetically identical and can develop in any way.

What is cell differentiation? Cell differentiation is the development of cells in different ways to carry out specific functions, making them more efficient.

How many distinct cell types are there in humans? There are 220 distinct cell types in humans, all of which develop by differentiation.

What is gene expression? Gene expression refers to the process of switching on a gene and using its information to make a protein or other gene products.

How do gradients of signaling chemicals help in differentiation? Gradients of signaling chemicals, like retinoic acid, help cells in the embryo determine their position and pathway of differentiation.

What does it mean for a cell to be totipotent? A totipotent cell can differentiate into any cell type, which includes the zygote and early-stage embryonic cells.

What is the difference between pluripotent and multipotent cells? Pluripotent cells can differentiate into many but not all cell types, while multipotent cells can differentiate into a limited range of cell types.

What is the stem cell niche? The stem cell niche is the specific location in a tissue where stem cells are found, providing a microenvironment necessary for their maintenance and differentiation.

What is the role of stem cells in muscle repair? Stem cells in muscle tissue remain inactive until injury occurs, at which point they proliferate and differentiate to replace damaged muscle tissue.

What are the properties of stem cells? Stem cells can divide repeatedly, have the ability to differentiate, and some can remain undifferentiated for long periods.

What are totipotent cells, and why are they important? Totipotent cells can differentiate into any type of cell, making them important for growing entire organs or tissues for medical uses.

What is the potential use of stem cells in regenerative medicine? Stem cells have the potential to regenerate tissues and organs, aiding in restorative surgery and therapeutic uses.

What is the surface area-to-volume ratio in relation to cells? The surface area-to-volume ratio is crucial for efficient absorption of substances and removal of waste in cells.

How does a smaller surface area-to-volume ratio affect cells? If the surface area-to-volume ratio is too small, substances will not enter the cell fast enough, and waste products may accumulate.

How do red blood cells have an efficient surface area-to-volume ratio? Red blood cells have a biconcave disc shape, which gives them a large surface area for oxygen exchange.

What are the adaptations of proximal convoluted tubule cells in the kidney? Proximal convoluted tubule cells have microvilli on the apical membrane and infoldings on the basal membrane to increase surface area for selective reabsorption.

How do the alveoli in the lungs aid in gas exchange? Alveoli are tiny air sacs with a large surface area and a thin cell wall, allowing efficient diffusion of oxygen and carbon dioxide.

What are the main functions of type I pneumocytes in the alveoli? Type I pneumocytes are adapted for efficient gas exchange due to their thin structure and minimal cytoplasm.

What is the role of type II pneumocytes in the alveoli? Type II pneumocytes secrete surfactant, reducing surface tension in the alveoli and preventing collapse.

How does the structure of skeletal muscle cells enable movement? Skeletal muscle cells are long, cylindrical, and striated, with many nuclei, enabling them to contract and produce force

What is the role of myofibrils in muscle fibers? Myofibrils are cylindrical structures within muscle fibers that contain alternating light and dark bands responsible for muscle contraction.

How do cardiac muscle cells differ from skeletal muscle cells? Cardiac muscle cells are shorter, branched, have a single nucleus, and are connected by intercalated discs, allowing synchronized contraction.

What is the purpose of intercalated discs in cardiac muscle? Intercalated discs allow rapid electrical signal propagation between cardiac muscle cells, ensuring synchronized contraction

How do egg cells provide resources for embryo development? Egg cells contain yolk for nutrition and mitochondria for energy production, supporting the developing embryo.