Homeostasis Flashcards
What is homeostasis?
The maintenance of a constant environment
-Involves constant changes around an optimum point
What is the importance of homeostasis?
-Changes in pH and temperature affect proteins e.g. enzymes
-Changes can cause a reduction in the rate of reaction
-Changes in water potential can change volumes in cells e.g expand or shrink
-Glucose concentration affects the glucose supply for respiration
How are the changes of homeostasis controlled?
-Optimum = point where reaction works best
-Receptor = detects change from optimum
-Coordinator = links the receptor and the effector
-Effector = muscle or gland which brings changes to return system to optimum
What is negative feedback?
-System deviates from optimum
-Change is detected by the receptor
-A change is then produced which returns the system back closer to the optimum
What is positive feedback?
-System deviates from optimum
-Change is detected by the receptor
-A change is then produced which causes an even greater deviation from the optimum
How are endocrine glands and hormones linked?
-Hormones are organic chemicals produced in an endocrine gland
-They travel in the blood and can be widespread or targeted
-Protein or peptide hormones e.g. insulin, ADH
-Steroid hormones e.g. oestrogen, progesterone
What are the glands?
-Hypothalamus
-Pituitary gland
-Thyroid gland
-Pancreas
-Parathyroid gland
-Adrenal gland
-Kidneys
-Ovaries
-Testes
How are hormones released?
Can be stimulated to release hormones by both nerves or other hormones
What is the link between the pituitary gland and the hypothalamus?
-Both located in the brain
-The hypothalamus often controls the pituitary gland
What is the pituitary gland?
-Controlled by the hypothalamus
-Produces 6 hormones from the anterior lobe
-Produces 2 from the posterior lobe
What is the thyroid stimulating hormone?
Controls the secretion of thyroxin from the thyroid gland
What is oxytocin hormone?
Stimulates the muscles of the uterus to contract during labour and stimulates the contraction of cells in the mammary tissue to release milk
What is antiduretic hormone (ADH)?
Decreases the urine volume and causes arteries to constrict after haemorrhage
What is prolactin hormone?
Stimulates and maintains the production of milk by mammary glands
What is the lutinising hormone (LH)?
Stimulates ovulation and formation of corpus luteum and prepares the uterus for implantation in females and stimulates the testes to produce testosterone
What is follicle stimulating hormone (FSH)?
Stimulates ovaries to produce oestrogen and stimulates the development of ova in females and stimulates the testes to produce sperm in males
What is ACTH hormone?
Controls the secretion of some hormones of the adrenal glands
What is the growth hormone (GH)?
Stimulates the growth of body cells and increases the build up of proteins
What happens in the pituitary gland and hypothalamus?
-Hypothalamus contains neurosecretory cells which produce secretions from the axons
-Cells 1 (group of neurosecretory cells) produce substances that stimulate or inhibit the release of hormones from the anterior pituitary
-They are known as releasing factors (if they stimulate) or release-inhibiting factors (if they inhibit)
-Neurosecretory cells 2 produce secretions that are stored in the posterior pituitary and released later as hormones
What is a second messenger?
-Hormones bind to a receptor on the target cell membrane
-Triggers a series of intracellular membrane bound reactions
-Stimulates the release of a second messenger
-The second messenger activates enzymes to alter the metabolism of the cell
What is the example of a second messenger (adrenaline)?
-Adrenaline binds to a receptor
-This activates an enzyme called adenyl cyclase which converts ATP to cyclic AMP (cAMP)
-cAMP acts as a second messenger
-Triggers different responses in the cell e.g. increased respiration and muscle contraction
What is oestrogen?
-A steroid hormone that can affect transcription by binding to a transcription factor
-Transcription factor is known as an oestrogen receptor
-Bind together to form an oestrogen to oestrogen receptor complex
-Moves to the nucleus where it binds to the promoter region before the target gene
-It then acts as a promoter
What is an oestrogen receptor?
-A transcription factor
-It regulates gene expression events that culminate in cell division
-Important for mammary gland development
How do hormones enter the cell?
-Pass through the membrane and bind to a receptor inside the cell
-They form a hormone receptor complex which passes through into the nucleus and acts as a transcription factor to regulate gene expression
What are tropisms?
The growth of a plant in a response to a directional stimulus
-they can grow away or towards a stimulus
What are the types of tropisms?
-Phototropic = shoot grows towards light
-Water = roots are positively hydrotropic
-Gravity = roots are positively gravitropic
How do plants grow?
-Cell division in plants occur in the meristem tissues in the tips of roots and shoots
-These areas are influenced by plant hormones
-E.g. auxins, gibberellins, cytokinins
What is apical dominance?
-High levels of auxins = a high level of abscisic acid which stops lateral bud growth
-High levels of auxins = a lower the level of cytokinins which reduce bud growth
What is an auxin?
-A plant hormone produced in the young shoots
-They move down to the roots
-The movement involves active transport and calcium ions
What are auxins involved in?
-Apical dominance to suppress the growth of lateral shoots so that one main stem grows the fastest
-Promoting root growth
-Tropic response of plant shoots to unilateral light
What happens when leaves drop off to reduce transpiration?
More cytokinins = more nutrients to leaves
-In Autumn the levels of cytokinins decrease so leaves die and drop off
-Auxins usually keep leaves on trees so when auxins decrease in Autumn the leaves drop off
How does IAA work?
-Cells in the shoot tip produce IAA
-IAA diffuses back down to the zone of elongation
-IAA molecules bind to specific receptor sites on the cell membrane activating the active pumping of hydrogen ions into cell wall spaces
-This changes the pH to 5 which is the optimum for enzymes to break bonds between the cellulose microfibrils
-This means the cell can absorb more water by osmosis causing cell walls to stretch meaning cells will elongate and expand
Why do shoots grow towards the light?
-When a shoot is exposed to light, auxins diffuse to the dark side
-There is a greater concentration of auxins in the zone of elongation on the dark side
-Stimulates these cells to grow and so the shoot grows towards the light
-Once the shoot is growing the transport becomes asymmetric (same on both sides of the shoot) and the shoot continues to grow towards the light
What do gibberellins do?
-Growth regulation
-Stimulate elongation of growing cells
-Promote growth of fruit
-Break dormancy of seeds
-Stimulate the formation of enzymes in germination
-Stimulate bolting (a period of sudden growth and flowering)
What is the role of gibberellins in seed germination?
-Seed absorbs water and swells
-Embryo secretes gibberellins that diffuse to the aleurone layer
-Gibberellins stimulate aleurone layer to produce amylase that diffuses into endosperm and breaks down food stores to provide embryo with materials for respiration and growth
-Enzymes produced in response to gibberellins digest the endosperm
What is the role of cytokinins?
-Promote cell divisions in the roots and shoots and cambium
-Promote lateral bud development
-Work with ethene in the abscission of leaves, flowers and fruits
What is phytochrome?
A blue/green pigment inside plans which exists in two interconvertible forms
-Pr = biologically inactive form which absorbs red light
-Pfr = biologically active form which absorbs far red light
What is the conversion of phytochromes?
-When one form of the pigment absorbs light it is converted reversibly into the other form
-When Pr absorbs red light it is converted into P
-When Pfr absorbs far red light it is converted back to Pr
-In the absence of red light Pfr gradually converts back to Pr
What is the time of conversion of phytochromes?
The length of time it takes for the conversion of pigments depends on the light intensity
-In low light intensity, conversion takes minutes
-In high light intensity, it takes seconds
-In the dark, Pfr is converted to Pr very slowly
What is the link of phytochromes and growth?
-During the day, levels of Pfr rise because sunlight contains more wavelengths so the conversion of Pr to Pfr occurs quicker than the conversion of Pfr to Pr
-During the night, levels of Pr rise because red wavelengths aren’t available in the dark and Pfr converts slowly back to Pr
What is the link of phytochromes and flowering?
-Enable plants to respond to environmental cues, e.g. photoperiodism (the reaction to plants to daylight)
-Effects the flowering of plants
What is the three main types of plants?
-Long day plants where Pfr stimulates flowering
-Short day plants where Pfr inhibits flowering
-Day neutral plants which have different flowering triggers
