Cell specialization

Outline the location and the function of stem cell niches in adult humans

• Bone marrow- inside bones. Produces blood cells (white/red cells and platelets) from hematopoietic stem cells (undifferientiated blood cellls)

• Skin stem cell- base of epidermis (outermost layer of skin) and hair follicles (tube-like structure of hair). Replaces damaged/dead skin cells and helps heals wounds

• Intestinal stem cell- base of intestinal lining (crypts). Regenerates lining of gut every few days

• Brain (neural niche)- Specific areas like hippocampus. Forms new neurons/suport cells for learning/memory

• Muscle stem cell- Between muscle fibers. Repairs/regenerates muscle tissues after injury

Outline the structure and function of straited muscle fibres

• Alternate dark and light bands = straited

• Fibres are surrounded by sacrolemma (single plasma membrane sheath around muscle fibre)

• Attatched to moveable parts of skeleton

• Muscle attatched by tendons and work in atagonistic pairs (one shortens, other stretches)

• Long, cylindrical shape

• Unbranched, very long, multinucleated

• Made of muscle fibres that includes:

  • Syncytial = fused with multiple cells into single functional unit with shared cytoplasm and multiple nuclei for rapid communication and coordination of contraction

  • Contractile proteins in cytoplasm.

  • Specilaised cytoplasm (sacroplasm) that contains mitochondria (produces ATP for muscle contraction) and myrofibrils (bundles of actin and myosin filaments which slide past eachother in contraction)

  • Specialized ER called sacroplasmic reticiulum that stores calcium and conveys signals to all parts of fibre at once using protein prumps

• Sacrolemma (muscle fibre membrane) that has tube-like projections that fold in from its outer surface aka transverse system tubules (T-tubules) for quick action potential

Define zygotes, morula, blastula, and blastocyst

Zygtote: Single diploid cell formed when 2 haploid (sperm and egg) are fused in fertilization.

Morula: Solid ball of cells formed after zygote undergoes several rounds of cell division

Blastula: Hollow ball of cells that forms from morula.

Blastocyst: Multicellular sac like structure surrounded by a single cell layered membrane with 107 cells inside (inner cell mass). The inner cell mass are all undifferentiated and unspecialized embryonic stem cells that can be differentiated into 200 types of cells that can form different tissues, organs, oragan systems, and organisms

List from smallest to biggest: organs, organism, tissues, cells, organ systems

cells, tissues, organs, organ systems, organism

Explain how the structure of a plant root hair cell supports efficient absorption of water and minerals.

• Large SA to V ratio because of elongated projection

• Thin cell wall reduces distance for substances to travel

• Numerous mitochondria = provide ATP through cellular respriation.

• ATP used for active transport of mineral ions against cocnentration gradient

• Cell membrane contains specific transport proteins/channel proteins for selective uptake of water and minerals

Outline the structure of sperm cells and how it helps its functions

• Compact nucleus head contains haploid genetic material

• Acrosome contains digestive enzymes to break down egg cell membrane

• Multiple mitochondrias in the midpiece/neck region. These provide ATP for flagella movement

• Tail is very long flagellum that generates force needed for forward motion in 9+2 mictrobules arrangement

• The head has a streamline/hydrodynamic shape that aids swimming through female reproductive tract. It is very narrow as its nucleus has tightly packed chromosome and small cytoplasm volume so resistance is low.

• Binding proteins in inner acrosomal membrane that is revelaed after exocytosis of the acrosome that binds proteins to the plasma membrane of the egg cell for the fusion of membrane and entry of sperm nucleus into the egg

Outline the structure of egg cells

• Surrounded by jelly layer (zone pellucida) that hardens to prevent polyspermy (ovum penetrated by multiple sperms for embryo development)

• Exterior follicle cells nourishes/protects the ova

• Protein cell surface receptors on egg’s surface that recognize and binds with correct sperm

• Cytoplasm is rich in nutrients for developing embryo after fertilisation

• Veiscles/cortical granules

• Large size to store nutrients, cytoplasm, and organelles for inital stages of embryonic development

• Haploid nucleus that cotnains half the number of chromosomes (23) to fuse with sperm for zygote formation

• Zone pellucida is thick membrane that surrounds the egg

List the adaptations for convoluted tubule cells to function

• Found in outer region of kidney.

• Responsible for reabsorption of vital substances (glucose/mineral ion) and filters out the blood in kidney.

• Microvili in apical membrane which enhances the surface area for more absorption. It is in the apical membrane in which many transporter proteins are located to move molecules/nutrients to absorb substances from the tubular fluid.

• Inbavinations (infoldings in basal membrane) = increase SA for solute reabsorption and secretion

• Wall is only one cell thick = inner apical membrane is in contact with the outer basal membrane which are close to blood capillaries

Distinguish between stem cells and fully differentiated cells

Stem cells:

• Are not differentiated

• Able to divide and differentiate into various specialized cell types

Fully differentiated cells:

• Lost its ability to differentiate into other types of cells

• Specialzed cells with specific functions

Explain how the structure of a ciliated epithelial cell allows it to move substances across the surface.

• Found in the respiratory tract and reproductive ssytem in females.

• Cilia/hair-like structures are present on surface

• These beat/move in coordinated manner that generates a wave-like motion

• It moves substances like mucus across epithelial surface in specific direction

• This allows it trap dust or other substances that one breathes and move them toward nostrils so it does not go into the lungs

List the properties that make skeletal muscle fibres irregular cells

• Does not follow usual pattern of cell division

• Does not expand by producing more cell in adults, instead it fuses with existing fibres

• If fibres are severely damages it does not undergo apoptosis (cell death) and cell replacement

List the limitations of cell size

• Surface area to volume ratio decreases as cell size increases

• Increases in cytoplasmic volume increases metabolic demands

• More transport proteins are present in arger cells membrane

Define morphogens

Signal molecules that controls cell differentiation. Occurs in gradients (concnetration difference area) in different regions of an early embryo. This concentration controls the regional development of the first cells into head and tail structures. Gradient of signallling molecule results in different parts of embryo development into different features.

As embryo developes = other signalling molecules becomes factors in differentiation.

List how red blood cells are adapted to carry out its function

• 8µm in diamter

• Contains haemoglobin that combines with and releases oxygen

• Has biconcave disc shape for more surface area for oxygen absorption = lower volume than sphere of same diamter

• Lack mitochondria and nucleus to hold more oxygen

• Flexible and have limited size as it can move through narrow blood capillaries

List how white blood cells are adapted to carry out its function

• Bigger than red blood cells for nucleus, granules, organelles, and mitochondria

• Retains nucleus

• Different types of white blood cells have different functions

• Many have vesicles with enzymes that kill microorganisms or phagocytosis

List how nerve cells are adapted to carry out its function

• Different neurons each have specialized roles

• Motor neurons carry impulses from brain or spinal cord so muscles can react.

• Motor neurons have long fibres (axons) that carry impulses up and down body over long distances (up to 1m) for efficient/rapid transmission of nerve impusles from brain to spinal cord to muscles

Distinguish between totipotent, pluripotent, multipotent, and unipotent stem cells

Totipotent: Can differentiate into any cell type (placenta and other extraembryonic tissues). May form complete organism.

Pluripotent: Cell types within the three germ layers (ectoderm, mesoderm, endoderm). Not extraembryonic tissues. Can’t form complete organism.

Multipotent: Cell differentia into limited number of cell types within specific tissues/organ.

Unipotent: Only forms single cell type such as sperm cells in mammals.

Distinguish between embryonic stem cells and adult stem cells

Embryonic: Undifferentiated cells that is capable of continous cell division and developing into all cell types of adult organism. Majority of embryo.

Adult: Replaces dead/damaged cells like bone marrow, brain, and liver.

Define stem cell niches and provide examples

Speciifc microenvironments in body that has stem cells or promote proliferation/differentation.

Examples include: bone marrow and hair follicles

Outline why the female gametes (egg) in humans is much larger than the male gamete (sperm)

Egg cells’ large volume allows large quantities food reserves to be stored in the cytoplasm.

Explain why the surface area to volume ratio is important in cells

The ratio limits the cell size. The rate of heat/waste production, resource consumption depends on the volume. A cell with more surface area per unit volume can move more materials in and out of cell.

As width of object increases, surface area increases but at slower rate than volume because surface area is squared while volume is cubed.

Larger cell = smaller surface area.

Describe the advantages of the adaptaion to increase surface area to volume rate of cells.

• Faster diffusion as rate of diffusion is directly proportional to surface area and inversely proportional to the distance

• Improved cellular communication

• SA affects rate mateirals enter/leaves cell

• Volume affects rate of materials use/produced by cell

• Bigger cell = smaller SA: V ratio = less diffusion that can’t exhange mateirals fast enough = low rates of metabolism

List the adaptations of type I and type II pneumocytes in alveoli

Type I: Thin and flat in shape to increase SA and minimize diffusion distance. Tightly joined to eachother so fluids can’t enter the alveoli from capillaries. Capillary walls are one cell thick to maximise rate of diffusion

Type II:

• Produces pulmonary surfactant which reduces surface tension and prevents alveoli from collpasing and sticking to eachother during breathing process.

• Pulmonary surfactant also aids in gas exchange as the moisture allows oxygen to dissolve before diffusing into the blooad and CO2 diffueses from moist surface before it is removed in exhalation.

• Rounded cells for larger cytoplasmic area for organelles. Oriented towards alveolar sac, increasing surface area and allows more surfactant secretion.

• Abiility to transform into type I when needed.

• Cytoplasm has many organelles for pulmonary surfactant production and secretion like secretory vesicles (lamellar bodies) that secretes a solution to coat epithelium of alveoli (both pneumocytes)

Outline the strucure and function of cardiac muscles

• Only in heart

• Specilazed straited muscle

• Myogenic = contract without external stimulation from nerves/hormones = heart can beat at its own regular intervals (length is regulated by nervours and endocrine system)

• Does not tire/fatgue = works thorughout individual’s life

• Single nucleus per fibre/cell

• Connected at ends by intercalated discs

• Branched and interconnected for rapid/coordinated transmission of electrical impulses

• High number of mitochondria to provide energy needed for continuous contraction

List the advantages and disadvantages of embryonic stem cells

Advantages:

• Low levels of DNA methylation than differentiated cells = more plasticity and potential for differentiation

• Pluripotency = differentiate into any cell type in body

• Therapeutic application (Parkinson, Alzheimers, diabetes, etc.)
  

Disadvantages:

• Higher risk of developing tumours

List the advantages and disadvantages of cord blood stem cells

Advantages:

• Higher match rate

• Wide range of application for wide variety of blood related diseases

• Can be stored = readily available when needed

Disadvantages:

• Limited capacity to differentiate into different cell types

• Limited cell volume

List the advantages and disadvantages of adult stem cells

Advantages:

• Adult stem cells are obtained by their own body = no ethical issues

• Lower risk of immune rejection (own body)

Disadvantages:

• Difficult to obtain

• Limited range of cell types

Describe the role of muscle cells in motility and how their specialized structure enables contraction.

• Muscle cells produce force and motion through contraction

• It contians myrofibrils which are made of repeating sacromeres (contains actin and myosin filaments)

• When it contracts, mysoin heads bind to actin filaments and pulls them inward which requires ATP for energy

• Sacroplasmic reticulum contains calcium ions that are released in response to nerve impulse. Calcium binds to troponin (protein complex in heart) that causes conformational change (modification) that enables myosin-actin binding.

Explain the relationship between form and function in the specialization of cells and its importances

• Form of cell directly related to its function

• Specialized cells have specific shapes/structures adapted to their roles

• Cell specializtion allows division of labor in organism which increases organism’s efficieny and thus survival

• Different cells perform specific functions more effeciently than generalized cells due to its specific structure (more specific adaptations that best fits their roles)

• Specialized cells work together in tissues/organs that allows complex functions that would not have been possible with only 1 cell

• Increased efficiency leads to better homeostasis, growth, and reproduction