biology4alevel600

 1 Animals and plants have internal communication systems that allow information to pass between different parts of their bodies, and so help them to respond to changes in their external and internal environments.  2 Mammals keep their internal environment relatively constant, so providing steady and appropriate conditions within which cells can carry out their activities. This is known as homeostasis.  3 Homeostatic equilibrium requires receptors that detect changes in physiological parameters such as the temperature, water potential and pH of the blood. Effectors are the cells, tissues and organs that carry out the functions necessary to restore those parameters to their set points. Homeostatic control systems use negative feedback in which any change in a parameter stimulates actions by effectors to restore the parameter to its set point.  4 Excretion is the removal of toxic waste products of metabolism, especially carbon dioxide and urea. The deamination of exces...

Gibberellins are plant growth regulators that are synthesized in most parts of plants (mainly in young leaves and seeds and in stems). They have a role in seed germination and controlling stem elongation . Stem elongation The height for some plants is partly controlled by their genes. Tallness in pea plants is affected by a gene with two alleles Le/le 1. dominant allele Le : codes for the functional enzyme of the active form of gibberellin GA1 --> stimulates cell division and cell elongation plant grows tall 2. recessive allele le: caused by a substitution mutation (alanine to theorine amino acid) homozygous recessive lele : no active form of gibberellin plant remains short Seed germination : of wheat and barley Seeds are dormant (waiting for the optimum condition) when first shed from parent plant. It contains very little water and is metabolically inactive. Absorption of water stimulates germination Embryo synthesizes gibberellin in response to water uptake Aleurone laye...

Chemical communication in plants Plant hormones or plant growth regulators are: - produced in a variety of tissues - move from cell to cell (by diffusion or active transport) or carried in xylem sap and phloem sap The two types we're going to look at auxin and gibberellin . Auxin Synthesized in meristems (the growing tips of shoots and tips of roots, where cell division occurs). It gets actively transported away from the meristems, from cell to cell and via phloem sap. Function: controlling growth cell division: mitosis cell elongation (by absorption of water; auxin is involved) cell differentiation Mechanism of auxin 1. Auxin binds to receptor 2. Stimulates ATPase to pump H +  across the cell surface membrane (from cytoplasm to cell wall, therefore lowering the pH of the cell wall)  3. Potassium ion channels stimulated to open; K +  move into the cytoplasm, therefore lowering the water potential inside the cytoplasm --> water moves into the cytoplasm via osmo...

The Venus fly trap is a carnivorous plant that obtains a supply of nigtrogen compounds by trapping and digesting small animals, mostly insects. Anatomy of the Venus fly trap Midrib = hinge 2 lobes glands that secrete digestive enzymes 3 sensory hairs on each lobe that respond when they are deflected nectar-secreting glands to attract insects stiff outer-edges that interlock to trap insects Electrical communication in plants microelectrodes in leaf cells detect changes in potential difference. depolarisation results from the outflow of Cl - repolarisation is achieved by the outflow of   K + action potentials travel along cell membranes, from cell to cell through plasmodesmata these action potentials last longer and travel more slowly than in animal neurones 1. Sensory hair is deflected 2.  Ca 2+  channels at the base of the hair opens . Ca 2+ flows in and generates a receptor potential . 3. Within 20 - 35 seconds, if 2 hairs get stimulated or 1 hair is stimul...

‘ Birth control ’ means taking control over if and when a couple have a child. It may involve: - contraception to prevent fertilisation -  use of hormones to prevent pregnancies 1. The birth control pill The pill contains steroid hormones that suppress ovulation . These synthetic hormones break down more slowly in the body so they act for longer; they are taken as oral contraceptives type 1: progesterone only type 2: progesterone and oestrogen combined The woman takes one pill daily for 21 days and then stops for 7 days during which time menstruation occurs. oestrogen and progesterone suppress the secretion of FSH and LH from the anterior pituitary gland (negative feedback effect). This prevents the concentrations of FSH and LH from reaching levels that would stimulate ovulation. after 21 days, concentration of oestrogen and progesterone fall (inactive pills taken). The uterine lining is no longer maintained and menstruation occurs Progesterone may allow ovulation to occur...

Hormones like adrenaline, insulin, glucagion and ADH - cell-signalling molecules - made in endocrine glands ; glands are groups of cells that secrete (produce and release) one or more substances - passed directly into the blood Steroid hormones are lipid soluble  à  pass through phospholipid bilayer and binds to receptor molecules inside the cytoplasm/nucleus and activate processes Menstrual cycle: changes that reoccur in the ovary and uterus every 28 days involving: ovulation menstruation : the breakdown and loss of the uterus lining * uterine cycle and ovarian cycle are synchronized The menstrual cycle is coordinated by glycoprotein hormones secreted by the anterior pituitary gland and ovaries 1. During menstruation, the anterior pituitary gland secretes follicle stimulating hormone (FSH) luteinising hormone (LH) Concentrations of FSH and LH increase over the next few days à control activity of ovaries – responsible for ovulation 2. In the ovary, one follicle beco...