1  Define the term stem cell  Define the term differentiation, with reference to the production of erythrocytes and neutrophils derived from stem cells in bone marrow, and production of xylem vessels and phloem sieve tubes from cambium  Explain the meaning of the terms tissue, organ and organ system. Candidates should be able to:

Cells make up TISSUES, groups of similar cells performing a common function e.g. Xylem or phloem in plants, muscle or nervous tissue in animals Groups of different types of tissues are arranged together to form ORGANS e.g. the stomach consists of epithelial, muscular and glandular tissue Organs are grouped into ORGAN SYSTEMS e.g. respiratory system, reproductive system. Organ systems consist of a number of organs working together to perform an overall life function 2

Stem Cells Stem cells are genetically identical, undifferentiated cells that carry a full set of genetic information, and are capable of dividing to become genetically identical new (daughter) cells, which can then differentiate to become specialised into any of the different cell types found in the organism.

4  Stem cells have a unique ability to renew themselves and give rise to the more specialized cell types that do the work of the body.  Stem cells remain unspecialized until a signal from the body tells them to develop into specific cells of the body like a heart, nerve, or skin cell  Differentiation is achieved due to the switching on and off of relevant genes

5  Totipotent Embryonic stem cells from a 8 cell stage embryo (morula)– able to differentiate into any type of cell, including embryonic cells Totipotent stem cells have a wide range of clinical applications  Pluriponent From the inner cell mass of an embryo (blastocyst) and umbilical cord blood – able to differentiate into most types of cells but not embryonic cells Narrow range of clinical applications  Unipotent cells - adult stem cells Able to differentiate into only one cell type – its own type

6 1Self renewal – they can continuously divide and replicate 2 Potency – they have the capacity to differentiate into specialised cell types Stem cells are unspecialised cells that have two key qualities

7  Cells destined to become erythrocytes (red blood cells) lose their nucleus, mitochondria, Golgi apparatus and rough endoplasmic reticulum.  They are packed full of haemoglobin and their shape is changed to become biconcave discs  Cells destined to become neutrophils retain their nucleus.  The cytoplasm of neutrophils makes numerous lysosomes and appears granular Erythrocytes and neutrophils perform different functions but contain the same genetic information. All blood cells are produced from undifferentiated stem cells (adult/unipotent) in the bone marrow. Particular genes are switched on/off so they differentiate to become specialised.

8 In plants meristem cells are like stem cells One type of meristem cell is the cambium The cambium in part of the vascular bundle and differentiates into transport tissues (xylem and phloem) To form xylem vessels, the cambium cells elongate produce lignin to strengthen and waterproof their walls – which causes cell contents to die so cells become hollow To form sieve tubes (phloem) the cambium cells elongate and multiply themselves ‘end to end’ the membrane/wall at the end of cells partially break down to create channels (for mass flow between cells) called sieve plates. To form companion cells (phloem), the cambium cells need to differentiate into cells which produce lots of enzymes and mitochondria (as cells does lots of reactions)

9 When asked to describe ‘specialisation’ of a cell you should: NAME THE FEATURE e.g. Sperm cells have a flagellum EXPLAIN HOW THE FEATURE ENABLES IT TO DO ITS ROLE e.g propels the sperm along the oviduct to meet an egg cell

10 Specialised Cells Specialised for defence against disease  Flexible shape – allows engulfing of foreign particles or pathogens by the process of phagocytosis (“cell eating”)  Migrates to and from the tissues, through pores in the capillary endothelium  Multi-lobed nucleus – allows flexibility  Contains many lysosomes – contain hydrolytic/digestive enzymes to break down engulfed particles.  Contains large amounts of rough endoplasmic reticulum – for protein (enzyme) synthesis  Granular appearance – contains granules - granules contain hydrolytic enzymes  Many receptor sites on the cell surface membrane for attachment to cells and pathogens (antigens) Multi-lobed nucleus (flexible) Granular (granules contain enzymes) Neutrophils (white blood cells; phagocytes) Phagocytosis

11  Haemoglobin requires iron for its structure as a respiratory pigment – O 2 is carried, from the lungs to the tissues bound to the iron in haemoglobin  Thin outer membrane - creates a short diffusion distance – allows rapid diffusion of oxygen into erythrocytes in the lungs (alveoli) and out of erythrocytes in tissues  Bi-concave disc shape - increases the surface area for diffusion of gases Allows more haemoglobin to be packed around the edge (in contact with capillary wall) – reduces the diffusion distance  Flexible membrane framework – allows red blood cells to squeeze through the narrow capillaries; ensures maximum contact between red cell membrane and capillary wall  No nucleus - there is more room for haemoglobin, with the whole cell full of haemoglobin Disadvantage – limits life span to ~ 120 days  Transports some CO 2 – from tissues to lungs Erythrocytes (red blood cells) - carry oxygen in the blood Contain haemoglobin (an iron containing respiratory pigment) to transport O 2 to tissues (cells) from the lungs

12  Nucleus contains half the number of chromosomes of an adult somatic (body)cell in order to fulfil its role as a gamete  Streamlined head and body – to reduce resistance during movement through fluid  Head contains genetic information (DNA) in the haploid nucleus, and an acrosome (lysosome). Acrosome contains hydrolytic (digestive) enzymes – digests the egg cell membrane for the penetration of the sperm head (nucleus)  Cell surface membrane in head region has receptors for binding to egg cell surface membrane  A flagellum (tail) to propel the sperm to the egg  Mid-piece is packed with mitochondria – to generate energy (ATP) for movement of flagellum Sperm cell (male sex cell; male gamete) Specialised to fertilise the ovum (female gamete) Fertilisation – fusion of male and female gamete to form a zygote – fusion of sperm and egg nuclei Sperm (n) + Egg (n)Zygote (2n) (haploid) (haploid) (Diploid) Sperm head entering an ovum

13  Packed with chloroplasts containing the light absorbing pigment chlorophyll  Converts light (solar) energy to chemical energy – i.e. synthesis of glucose (organic) from inorganic materials (CO 2 and H 2 O) using light energy of the sun  Regular shaped, closely packed columnar palisade cells forming a continuous layer for maximum absorption of sunlight.  Thin walled cells – for rapid diffusion of gases (carbon dioxide and oxygen).  Chloroplasts can move within the cell, aided by the cytoskeleton– for maximum light absorption  Vacuole – membrane bound organelle containing cell sap; helps to maintain turgidity to support plant  Cellulose cell wall – protects the cell, confers strength, and prevents the cell from bursting Palisade mesophyll cells Leaf palisade mesophyll cell Specialised to carry out photosynthesis Lower epidermis Vascular bundle Air space Upper epidermis Xylem Phloem Sunlight

14 Cross-section of leaf

15  Regulate the size of leaf pore – allow entry and exit of gases and water vapour  Change shape easily  Swell up when the vacuole is filled with water and become turgid (firm)  In light (photosynthesis) - K ions are moved into the guard cell actively – water follows down a water potential gradient and – makes the guard cells turgid. ATP for active transport Contain mitochondria to generate ATP for active transport  This causes the thin outer walls to stretch and the thickened inner walls to bend outwards – opening the stomata – allowing gas exchange for photosynthesis.  When flaccid (e.g. in the dark – when there Is no photosynthesis), the thickened inner walls move inwards to close the stoma Guard cells Specialised to open and close leaf pores (stomata) – used for gas exchange and transpiration (loss of water vapour from leaves by evaporation) Stoma (pore) Guard cells Stomata on underside of leaf

16 The thick inner wall ensures that only the outer wall stretches when the cell is turgid – causing the inner wall to curve outwards, thus opening the pore Guard cells turgid (firm) - during daylight Guard cells flaccid (limp) - at night (dark)  Potassium (K) ions are actively transported into guard cells during daylight (photosynthesis)  Reduces the water potential inside the guard cells  Causes water to enter down a water potential gradient by osmosis  Guard cells fill with water and become turgid  Stomatal pores open  In the dark (night), K ions are actively pumped out of guard cells– causing water to leave by osmosis – guard ells become flaccid and the pores are closed Dark Light

17  Provide a large surface area for efficient absorption of water by osmosis down a water potential gradient  Minerals are absorbed by active transport against a concentration gradient  Some minerals are transported down a concentration gradient from the soil by facilitated diffusion through channel proteins  Cell wall of root hair cell is thin and permeable – reduces diffusion distance  Large number of mitochondria in root hair cells provide energy (ATP) for the active transport proteins located in the cell surface membrane Root hair cell Numerous, long hair-like extensions of the cell wall and cell membrane of root epidermal cells in young plants, extending into the soil Specialised for absorbing water by osmosis and dissolved minerals by active transport and facilitated diffusion from the soil into the root

18  Water and dissolved minerals from the soil are taken up into root hairs  Water enters root hair cells by osmosis  Mineral ions are taken up by active transport and diffusion ( facilitated )

19  Retinal cells – replace dead cells in retina to cure diseases like glaucoma  Skin cells - graft new skin cells to replace damaged cells in burn victims  Nerve cells - repair damage caused by spinal injuries to enable paralysed victims to regain movement  Blood cells – bone marrow transplants for cancer patients who are immuno-compromised as a result of chemotherapy Some therapeutic uses of stem cells