Cell Diveristy and Cell Differentiation Flashcards
Why do multicellular organisms need specialised cells?
They are larger and have a smaller SA/V ratio meaning most of their cells are not in direct contact with the external environment so they need them to carry out particular functions
What is a stem cell?
An unspecialised cell able to express all its genes in its genome and divide by mitosis
What is differentiation?
The process by which stem cells become specialised into different types of cell
How do embryonic cells differentiate thus becoming specialised for a particular function?
Certain genes are switched off and other genes are expressed more so that:
The proportions of the different organelles differ from those of other cells
The shape of the cell changes
Some of the contents of the cell changes
Name two specialised animal cells in mammals and their function
Erythrocytes which carry oxygen from the lungs to resourcing cells
Neutrophils which ingest invading pathogens
How are erythrocytes adapted to carry out their function?
Biconcave shape increasing their SA/V ratio meaning O2 can diffuse across their membranes and easily reach regions inside the cell
Flexible due to their cytoskeleton allowing them to change shape as they travel through capillaries
Most of their organelles are lost at differentiation providing space for haemoglobin molecules housed inside them
How are neutrophils adapted to carry out their function?
They are attracted to and travel towards infection sites by chemotaxis
They can ingest invading pathogens by phagocytosis
Multilobed nucleus
How are spermatozoa specialised?
Many mitochondria to carry out aerobic respiration - ATP produced provides energy for the tail to move and propel the cell towards ovum
Small, long and thin
Enzymes released from the acrosome at an ovum digest the outer covering of the ovum allowing the sperm head to enter
Sperm head contains haploid male gamete nucleus and very little cytoplasm
What are epithelial cells and how are they adapted to carry out their function?
Cells that constitute lining tissue
Squamous epithelial cells are flattened in shape
Many epithelial cells have cilia to move mucus
What are some examples of specialised plant cells?
Palisade cells - closely packed photosynthetic cells within leaves
Guard cells - cells that surround stomata
Root hair cells - epidermal cells of young roots with hair life projections
Xylem - tubes which carry water up a plant
Phloem - tissue that carries assimilates within plants
How are palisade cells within leaves adapted for photosynthesis?
Long and cylindrical - pack together with a little space between them for air to circulate, CO2 in the spaces diffuses into the cells
Large vacuole so chloroplasts are positioned nearer the outer edge of the cell, reducing CO2 diffusion distance
Many chloroplasts for photosynthesis
Cytoskeleton threads and motor proteins to move chloroplasts depending on sunlight intensity
Where are guard cells found?
Within the lower epidermis in leaves
Why can’t guards cells carry out photosynthesis even though they contain chloroplasts?
They don’t have the enzymes needed for the light independent stage of photosynthesis
Name and describe the function of guard cells
Gaseous exchange -
Light energy is used to produce ATP
ATP actively transports potassium ions from surrounding epidermal cells into guard cells, lowering water potential
Water enters the guard cells from neighbouring epidermal cells by osmosis
Guard cells swell and becomes more rigid , the tips bulge and the stoma enlarges
As the stomata open, air enters the spaces within the cells
Gaseous exchange occurs and CO2 diffuses into the palisade cells (these cells use it for photosynthesis so conc gradient maintained)
O2 produced during photosynthesis can diffuse out of the palisade cells into air spaces and out through open stomata
How are root hair cells adapted for their function?
Hair-like projection increases surface area for absorption of water and mineral ions from the soil
Mineral ions are actively transported into the cells lowering the water potential, causing water to follow by osmosis down water-potential gradient
Special carrier proteins in the plasma membranes in order to actively transport the mineral ions in
Produce ATP for active transport
What is a tissue?
A group of similar cells working together to perform a specific function
What are the four main tissue types in the body?
Epithelial tissue
Connective tissues that hold structures together and provide support
Muscle tissues made of cells specialised to contract and cause movement
Nervous tissues made of cells specialised to conduct electrical impulses
What is the function of epithelial tissues?
Protection
Absorption
Filtration
Excretion
Secretion
What are the characteristics of epithelial tissue?
Made up of cells that are very close to each other, adjacent cells bound together to form sheets
No blood vessels - cells receive nutrients by diffusion from tissue fluid in connective tissue
Some have smooth surfaces, some have projections
Short cell cycles, they divide daily to replace damaged tissue
What does connective tissue consist of?
Non-living extracellular matrix, containing proteins and polysaccharides, which separates the living cells within the tissue and enables it to withstand forces
What are examples of connective tissue?
Blood
Bone
Cartilage
Tendons
Ligaments
What are three types of cartilage?
HYALINE CARTILAGE which forms the embryonic skeleton, covers the ends of long bones in adults, joins ribs to the sternum and is found in the nose, trachea and larynx
FIBROUS CARTILAGE which occurs in discs between vertebrae in the backbone and in the knee joint
ELASTIC CARTILAGE which makes up the outer ear and the epiglottis
What does it mean if muscle tissue is ‘well vascularised’?
Muscle tissue has many blood vessels
What is the function of muscle tissue?
It allows movement
Myofilaments made of action and myosin allow the muscle tissue to contract
What are the three types of muscle tissue?
SKELETAL MUSCLE that are packaged by connective tissue sheets, joined to bones by tendons
CARDIAC MUSCLE which makes up the walls of the heat and allows the heart to beat and pump blood
SMOOTH MUSCLE which occurs in the walls of the intestine, blood vessels, uterus and urinary tracts and propels substances along the tracts
What is epithelial tissue in humans equivalent to in plant cells?
Epidermal cells
What are the characteristics of epidermal tissues?
Consists of flattened cells that lack chloroplasts and form a protective covering over leaves, stems and roots
Some have walls impregnated with a waxy substance, forming a cuticle that reduces water loss - important for plants that live in dry places
What is the function of vascular tissue?
Transport
What are the main types of plant tissues?
Epidermal tissue
Vascular tissue
Meristematic tissue
What are the functions of the two types of vascular tissue?
Xylem vessels carry water and minerals from roots to all parts of the plant
Phloem sieve tubes transfer the products of photosynthesis, in solution, from leaves to parts of the plant that do not photosynthesise
What is meristematic tissue?
Tissue that contains stem cells from which all other plant tissues are derived by cell differentiation
When is meristematic tissue found?
In areas called meristems - at root tips, shoot tips and in the cambium of vascular bundles
What are the characteristics of the cells in meristems?
Thin walls containing little cellulose
No chloroplasts
Small vacuole
Can divide by mitosis and differentiate into other types of cells
How do xylem derive from meristems?
Some cambium cells differentiate into xylem vessels
- Lignin is deposited in cambium cells to reinforce and waterproof them but this also kills the cells
- The ends of the cells break down so that the xylem forms continuous columns with wide lumens to carry water and dissolved minerals
How do phloem vessels derive from meristems?
Some cambium cells differentiate into phloem sieve plates or companion cells
- Sieve tubes lose most of their organelles and sieve plates develop between them
- Companion cells retain their organelles and continue metabolic functions to provide ATP for active loading of sugars into the sieve tubes
What is the definition of an organ?
A collection of tissues working together to perform the same function
What are the main plant organs?
Leaf - photosynthesis
Root - anchorage in soil, absorption of mineral ions and water, storage
Stem - support, holds leaves up so that they are exposed to sunlight, transportation of water, minerals and products of photosynthesis, storage of products of photosynthesis
Flower - sexual reproduction
What are some examples of animal organs?
Heart
Kidney
Liver
Brain
Optic nerve
Biceps muscle
Lungs
Eye
What is an organ system?
A number of organs working together to carry out an overall life function
What are some examples of organ systems in animals?
Digestive system
Circulatory system
Respiratory system
Urinary system
Integumentary system
Musculoskeletal system
Immune system
Nervous system
Endocrine system
Reproductive system
Lymph system
What are the characteristics of stem cells?
Undifferentiated so capable of becoming any type of cell in the organism - pluripotent
Able to express all their genes
Can divide by mitosis and provide more cells that can differentiate into specialised cells for growth and tissue repair
What are the different sources of stem cells?
Early embryos formed when the zygote begins to divide (embryonic stem cells)
Umbilical cord blood
Developed tissues amongst differentiated cells (adult stem cells)
Laboratories, developed by reprogramming differentiated cells to switch on certain genes and become undifferentiated (induced pluripotent stem cells)
Where can stem cells be used in research and medicine?
Bone marrow transplants
Drug research
Developmental biology
How can stem cells be used in bone marrow transplants?
To treat diseases of the blood and immune system
To restore patient’s blood system after treatment for specific cancer types - bone marrow can be obtained before treatment, stored then returned after treatment
How can stem cells be used in drug research?
If stem cells can be made to develop into particular types of human tissue, then new drugs can be tested first on these tissues rather than animal tissue
How can stem cells be used in developmental biology?
To develop a better understanding of how multicellular organisms develop, grow and mature
Scientists can study how cells develop to make particular cell types
Can learn how each cell type functions and see what goes wrong when they are diseased
