specialised cells Flashcards
(16 cards)
how do cells become specialised?
some genes are expressed while others are silenced due to cell differentiation mediated by transcription factors, cells produce proteins that determine their structure and function
what is a transcription factor?
a protein that controls the transcription of genes so that only certain parts of the DNA are expressed, e.g. in order to allow a cell to specialise
how do transcription factors work?
- move from cytoplasm into nucleus
- bind to promoter region upstream of target gene
- makes it easier or more difficult for RNA polymerase to being to gene, this increases / decreases rate of transcription
describe the 2 groups of specialised cells in blood
erythorocytes (red blood cells): biconcave, no nucleus, lots of haemoglobin to carry oxygen
leucocytyes (white blood cells): lymphocytes, eosinophils, neutrophils to engulf foreign material, monocytes
how do specialised cells in the blood form?
multipotent stem cells in the bone marrow differentiate into:
- erythrocytes, which have a short lifespan and cannot undergo mitosis since they have no nucleus
- leucocytes, including neutrophils
state the relationship between a system and specialised cells
- specialised cells -> tissues that perform specific function -> organs made of several tissue types -> organ systems
describe the structure of squamous and ciliated epithelia
simple squamous epithelium: single smooth layer of squamous cells - thin and flat with round nucleus - fixed in place by basement membrane
ciliated epithelium: made of ciliated epithelial cells - column shaped with surface projections called cilia that move in a synchronised pattern
describe the specialised structure of a spermatozoon
- specialised to fertilise an ovum during sexual reproduction in mammals
- haploid nucleus - so fertilisation restores diploid chromosome number
- acrosome secretes enzymes to penetrate ovum coat
- spiral-shaped mitochondrion
- flagellum bound by plasma membrane propels cell
describe the structure and function of palisade cells and guard cells in plants
palisade: specialised to absorb light energy for photosynthesis, so contain many chloroplasts, packed closely together
guard: form stoma, when turgid: stoma open, when flaccid: stoma close, walls are thickened by spirals of cellulose
describe the structure and function of root hair cells
- specialised to absorb water and low concentration minerals from soil
- hair like projections increase surface area for osmosis / carrier proteins for active transport
- many mitochondria produce ATP for active transport
describe the structure of a vascular bundle
- (refer to image)
- cambium / meristematic tissue
- phloem tissue on outside, xylem on inside
describe the structure of phloem tissue
- sieve tube elements: form a tube to transport sucrose in the dissolved form of sap
- companion cells: involved in ATP production for active loading of sucrose into sieve tubes
- plasmodesmata: gaps between cell walls, where the cytoplasm links, allowing substances to flow
describe the structure of xylem tissue
- vessel elements: lignified secondary walls for mechanical strength and waterproofing; perforated end walls for rapid water flow
- tracheids: tapered ends for close packing; pits for lateral water movement; no cytoplasm or nucleus
- parenchyma: packing tissue with thin walls transmit turgidity
- sclerenchyma fibres: heavily lignified to withstand negative pressure
describe the structure of cartilage
- avascular smooth elastic tissue made of chondrocytes, which produce extensive extracellular matrix (ECM)
- ECM mainly contains collagen and proteoglycan
- 3 categories: hyaline, yellow elastic, white fibrous -> category depends on ratio of cells : ECM
name the 3 types of muscle in the body and where they are located
cardiac: exclusively in the heart
smooth: walls of blood vessels and intestines
skeletal: attached to incompressible skeleton by tendons
describe the gross structure of skeletal muscle
- muscle cells are fused together to form bundles of parallel muscle fibres (myofibrils)
- arrangement ensures there is no point of weakness between cells
- each bundle is surrounded by endomysium: loose connective tissue with many capillaries
