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231/2 BIOLOGY PAPER 2 JULY/August 2014 Marking scheme: 1. a)i) (2mks) ii) Auxins/ produced by shoot and root tip accumulate on lower side of shoot and root due to gravity; higher concentration of auxins on lower side of shoot causes rapid growth; than upper side of the shoot. Therefore, the shoot bends upwards; higher concentration of auxins on lower side of the root inhibits rapid growth therefore the root bends downwards; (4mks) b) Use of a klinostat; (1mk) c) Phototropism that exposed leaves to maximum light for photosynthesis; Geotropism enables roots to extend deeply in the soil for anchorage; (any one 1mk) 2 a) i) Optimum temperature for maximum enzyme activity; Temperature below optimum level inactivate the enzymes/ temperature above optimum level denatures enzymes; ii) Optimum PH for maximum enzyme activity; enzymes are denatured by pH below optimum/ strong acid or alkalis; (2mks) b) When blood sugar level rises above normal. Insulin hormone is produced; insulin stimulate liver cells to convert glucose into glycogen. Also stimulate liver cells to convert glycogen into fats/ stimulates liver cells to increase oxidation of glucose; when blood sugar level falls below normal level, glucagon hormone is produced; glucagou stimulate the liver cells to convert glycogen to glucose; (4mks) 3 a) – Increase the number of aquatic animal; - Reduce the number of water weeds; - Cover the jar with alluminium foil to block light from reacting the water weeds; (any two 2mks) b) i) Carbon IV oxide was absorbed from water; and used for photosynthesis; without replacement. The PH of water rises; (3mks) ii) Carbon iv oxide was produced; by animals during respiration; this reduced the ph of water; (3mks) 4 a) Gene for red fur/colour and gene for white fur or colour are co-dominance; Acc: partial dominance /incomplete dominance (1mk) b) Parental genotype RW Parental Gamete X RR ; x F. Genotype F. phonotype Red Red Roan Roan Phenotypic Ratio Red Red : Roan 1 : 1 (4mks) 1 c) Plant breeding / Animal breeding Improvement of yields; (any 1) d) – Mutation; - Crossing over; - Fertilization; - Independent assortment of genes; Any two 2mk) 5 a) S-Pancrease; U- Duodenum; b) Emulsification of fats; to increase the surface area for reaction of lipase; provide alkaline PH; for action for pancreatic amylase; lipase; Trypsin; / Neutralize acidic chyme from stomach; to provide alkaline medium for efficient enzymatic activity; (Any four) (4mks) c) i) Pancreatic trypsin; pancreatic amylase; pancreatic lipase; (Any two) (2mks) ii) - Trypsin converts proteins to peptides; - Pancreatic amylase converts starch to maltose; - Pancreatic lipase converts lipids to fatty; 2 Acids and glycerol; (any two) (2mks) 6a) A-Intermittent /Discountinous growth; B- Continous growth; b) Rigid/hard exoskeleton; prevents growth; the exoskeleton is shed during moulting; this allows rapid growth ;to occur before the new exoskeleton hardens up; (4mks) c) Ecdysone/ moulting hormone; (1mk) (d) i) P&Q Slow rate of growth, due to small number of cells dividing; the young organism is still adapting to new environment; iii) Q & R - Rapid/ fast rate of growth; due to large number of dividing cells; - The organisms has adapted to the environment; (4mks) - No limiting factors like space, wastes e.t.c.; e) i) Internal fertilization; ii) Provide protection to the developing embryo from harsh environment; - Less number of gametes are involved./ No waste of gametes; - Developing embryo experiences little environmental changes; (Any two) f) i) Meiosis; ii) Crossing over; Synapsis/ formation of bivalents; (2mks) (1mk) (2mks) 7. A balanced diet refers to a meal (food) that contains all the nutrients (carbohydrates, proteins, lipids, vitamins, mineral salts and water) in their right proportion; A balanced diet is important to children because it contains:(i) Proteins that play the following roles in children:- Forms body structures; - Used in formation of enzymes; - Forms haemoglobin found in red blood cells; - Forms hormones used to regulate life processes; - Forms antibodies that provides immunity against diseases; - Is oxidized during starvation to release energy, ii) Carbohydrates that plays the following roles in children:- Provide energy required by children during oxidation; 2 iii) Roughage that plays the following roles:-Makes food to be bulk hence a child gets satisfied easily; - It promotes peristalysis which prevents constipation in children; iv) Lipids - are oxidized to release energy; - Forms part of the structure of the cell membrane; - Used as an insulator against excess heat loss in children/ - Used to form layers around organs which protect them from mechanical injury; - Act as a source of metabolic water - Stores various types of vitamins ie. Fat soluble v) Water - used to dissolve food; - It cools the body; - Provides a media for transport; Facilitates hydrolysis process; Maintains the shape of the cells; vi) Mineral salts includes:- Calcium for teeth and bone formation to prevent rockets - Phophorus for teeth and bone formation - Iodine used in formation of thyroid hormone which prevents goitre; - Iron used for haemoglobin formation that prevent anaemia; vii) Vitamins that play at the following roles:- Vitamins A prevent poor night vision in children; - Vitamin B1 prevents beriberi - Vitamin B2 prevents pellegra - Vitamin B12 used in formation of blood cells to prevent pernacious anaemia; - Vitamin C protects against infection that prevent scurvy - Vitamin D prevents rickets; - Vitamin E prevents sterelity; - Vitamin K prevents excessive bleedings; (Any 20) 8 The gaseous system in mammals includes the nostrils, trachea, bronchus, bronchioles, the lungs, the rib cage, the intercostals muscles, the diaphragm, the vertebral column; The Nostrils: Is lined with hairs that trap foregn particles in the hair; is lined with goblet cells that secret mucus which trap solid particles and pathogens; Tranchea / wind pipe - Made up of incomplete rings of cartilage a long its length which resist collapse when pressure is low in chest cavity; - The incomplete cartilage rings have gaps on the side facing the oesophagus which allow smooth swallowing; - It is lined with goblet cells that secrete mucus that trap foreign particles and pathogens; - It is lined with cilia which move mucus upwards into the pharynx; - Has epiglottis that prevents food entering into it during swallowing; Lungs - They are covered with pleural membrane; - The pleural membrane secrets pleural fluid that lubricates the lungs (reduce friction) during movement; - The lungs are elastic hence expand and contract to hold and expel large volume of air; - The lungs are made up of very many alveoli that gives a large surface area for gaseous exchange (70m2) - The alveoli are:- Moist which dissolve the diffusing gases; - Covered by a thin layer of wall for easy diffusion of gases a cross it; - Highly vascularised which enhances faster transportation of gases; Diaphragm - a muscular layer that contract and relax to facilitate inhalation and exhalation respectively; The ribcage -they protect the lungs from mechanical damage; Provide surface for the attachment of the intercostals muscles; The ricage and intercostals muscles forms an air-tight thoracic cavity that maintains constant air pressure; Intercostals muscles They contract and relax which changes the thoracic volume to enhance inhalation and exhalation in mammals; 3