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Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 54 Energy flow and the nutrient cycling in an ecosystem An ecos ystem comprises biotic and abiotic components which interact extensivel y with each other. Based on their ecological roles, the biotic components of an ecos ystem can be classified as : Producer : they are the green plants which absorb solar energy to s ynthesize complex organic compounds from simple inorganic substances by photos ynthesis, they act as the ultimate food source to all the heterotrophs : other producers are green algae and blue green algae, they are mainl y found in aquatic habitat, such as freshwater and marine water, they are the most important producers in earth (as 70% of the earth surface is covered with water). Consumer : they are heterotrophs which ingest other organisms or organic particles, they are mainl y animals a) primary consumer : they are the herbivores which feed on plants e.g. pond snail, insect larva and zooplanktons b) secondary consumer : they are the carnivores which feed on primar y consumers e.g. water beetles, tigers, etc. c) tertiary consumer : they are large carnivores which feed on the secondary and primary consumers as well as producers, e.g. man d) detritus consumer : they are detritivores (detritus feeder / scavengers) which feed on detritus that refer to the particulate organic matter involved in the decomposition of dead organisms, e.g. earthworm and crab etc. Decomposer : they are mainl y bacteria, fungi and some flagellates : by means of their saproph ytic activities, they decompose the eliminated products of animals and the dead bodies of the organisms into simple compounds : these compounds are absorbed as nutrients b y the green plants again : they enable the nutrients to be used continuousl y in a cyclic form in the ecos ystem : they are most abundant in the soil or water bottom where the dead bodies of plant and animals accumulate : when the temperature conditions are favourable, decomposition occurs rapidl y Energy and essential materials are therefore transferred from producers to consumers through the feeding processes. Eventuall y, decomposers break down the organic matter and release inorganic materials back to the environment. These inorganic materiasl are used b y the producers as nutrients again. Food chain : the transfer of food energy from producers through a series of organisms with repeated eating and being eaten Eco sy st e m P ro d uc er fr e s h wa ter p o nd green algae sea weeds grass green plants rock y pond Grassland Woodland P r i ma r y c o n su me r → → → → protozoa molluscs grasshopper caterpillars se c o n da r y c o n su me r → → → → mosquito larva starfish lizard sparrow Te rtiary c o n su me r → → → → fish sea birds snake hawk Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 55 Food web : in general, the food chains in an ecos ystem are not isolated, but are interconnected with one another, i.e. an herbivore may feed on several species of plants, and/ or be consumed by many consumers and so on, such a number of interconnected food chains is known as food web Trophic level : organisms in a food chain occupy different trophic levels, which indicate their place in the energy flow through the communit y : organisms whose food is obtained from plants by the same number of steps in the food chain belong to the same trophic level producers - first trophic level primary consumers - second trophic level secondary consumers - third trophic level tertiary consumers - fourth trophic level BS I 3 r d ed. p300 fig 10.2 Fig. 35 A simple schematic comparison of terrestrial and aquatic ecosystems Energy flow in the ecosystem I. Productivit y : Refers to the amount of energy or living materials fixed in a population, or a trophic level, or an entire ecos ystem in a given time a) gross primary productivit y : rate of dry matter production by photos ynthesis in an ecos ystem, it does not represent the actual amount of food potentiall y available to heterotrophs because some of the organic matters are used to meet plant respiration and metabolism Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 56 b) net primary productivit y : it is the biomass which is incorporated into a plant communit y during a specific time intervals, minus the part respired c) secondary productivit y : it is the rate of incorporation of biomass at the consumer levels during a specific time interval [Note] Production is the difference in biomass within a certain time interval. II. Energy flow : • as solar radiation passes through the biosphere, large parts are used to perform other functions, onl y small parts can be used in photos ynthesis Energy Dissipation Reflected Direct conversion to heat Evaporation, precipitation (drives hydrological cycle) Wind, waves and currents Photos ynthesis Total Percent / % 30 46 23 0.2 0.8 100 BS I 3 r d ed. p302 fig10.4 Fig. 36 Flow of energy and cycling of materials through a typical food chain. • the energy supplies for the grass, onl y a small part is used in the s ynthesis of organic materials, much are lost • part of the primary productivit y is used in the respiration of the producers, of the net primary productivit y, a portion is eaten by the primary consumers, the rest remains unused and is passed as dead plant materials • of the food eaten b y the primary consumers, some is assimilated and incorporated into the body tissue while others are unabsorbed and are discarded in the form of faeces and other wastes • the same loss of energy occurs when the energy is transferred from the primary consumers to the secondary consumers III. Ecological p yramids : The feeding relationships between organisms at different trophic level within a communit y can be represented by ecological pyramids. The producers (green plants) form the base of the p yramids can be structured according to numbers of organisms, total biomass, or total energy flow at each trophic level. Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 57 a) P yramid of numbers : the progressive loss of energy at each trophic level of a food chain puts a natural decrease on the total weight and total number of living organisms that exist at each successive level in the chain : the number of organisms in each trophic level is usuall y smaller than that of the one they are feeding on thus can be expressed in the form of a p yramid, called the pyramid of numbers : for diagrammatic purposes the number of organisms in a given trophic level can be represented as a rectangle whose length is proportional to the number of organisms in a given area 4 t h t r o p hic le v e l 3 r d t r o p hic le v e l 2 n d tro p hic le v el 1 s t t r o p hic le v e l Examples : Normal pyramid A tree is the producer, on which worms are the lived, that are eaten b y birds. A tree which is infested with parasites and the latter are parasitized by further parasites. Grasses are eaten by a cow which is infested with parasites. b) P yramid of biomass : the graphical representation of the trophic structure for a communit y of organisms in terms of the biomass [Note] Biomass is defined as the total dry weight of the total amount of living materials presented at a trophic level Fig. 37 Changes in standing crop biomass of producers and primary consumers and in certain environmental variables in a lake during one year. BS I 3 r d ed. p307 fig 10.8 Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 58 : two forms of p yramids of biomass can be constructed, the upright pyramid and inverted pyramid : if the producers support herbivores, and herbivores support carnivores then upright pyramid of biomass is the one we might expect : however an inverted p yramids of biomass is found in open water and deep water ecos ystem where the producers are small and short-lived, the phytoplanktons (producers) with smaller biomass can support the zooplanktons (primary consumers) with larger biomass because of their much rapid rate reproduction (high turnover rate) [Note] The data are collected only over a limited duration, thus the pyramids of biomass only indicates the amount of material presents over a very short period of time, and gives no indication of the total amount of material produced or the rate at which that material is being produced c) P yramid of energy : at each transfer of energy from one trophic level to the next higher, there is always a loss of energy from the s ystem : energy transformation is never 100% efficient and the living organisms in each trophic level required certain amount of energy for maintaining basal metabolic rate, for growth and reproduction and movement : it overcomes the difficult y encountered in pyramids of number and biomass, i.e. inverted pyramid never occurred here : it shows the total amount of energy utilized by the organisms in different trophic level in a square metre, over a given period of time, i.e. it shows the amount of new tissues of organisms produced in a unit time (productivit y) : it permits comparison of trophic structure of different ecos ystem e.g. a desert and a tree forest Exercise : (90 I 7b) Distinguish between production and biomass. [2 marks] (98 I 11) Why is the p yramid of energy always upright whereas the pyramid of biomass can sometimes be inverted ? [4 marks] IV Biogeochemical cycles : The fundamental difference between the flow of energy and the flow of materials in an ecosystem is that the latter can flow through the ecos ystem and be recycled again to be available to producers, e.g. the flow of energy in an ecos ystem is unidirectional while that of materials or nutrients is cyclic. The importance of decomposers in an ecos ystem is to allow the recycling of nutrients and makes it possible. Since they convert dead organic substances into forms which are available for the plants to use again. Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 59 a) Carbon cycle : it is the circulation of carbon atom between the carbon dioxide in the air and the complex carbon compounds (carbohydrates, proteins and lipids) in the tissues of living organisms Fig. 38 The carbon cycle. UB p391 fig 27.4 • removal of carbon dioxide from the air by green plants = by means of photos ynthesis and fix it as carbohydrates and later into other organic compounds animals = they feed on plants, removes the carbon dioxide indirectl y fossil fuels = millions of years ago, the dead remains of organisms in soil or compressed under water slowl y changed into fossil fuels such as peat, coal and petroleum, this fossilized carbon seems to be locked up underground and is lost from the free s ystem water bodies = carbon dioxide dissolves readil y in water as soluble calcium bicarbonate, this carbonate to form limestone or is absorbed by aquatic animals to form calcareous shells • return of carbon dioxide to the atmosphere by respiration = all living organisms respire to release energy and carbon dioxide which escapes back to the atmosphere decomposition = the excretory wastes of animals and the dead remains of organisms are decomposed by bacteria and fungi to form their own organic compounds, but at the same time carbon dioxide is also released combustion = in forest fire and the combustion of fossil fuels b y man, carbon dioxide is released into the atmosphere Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 60 volcanic activities = carbon dioxide is being continuousl y emitted from volcanic vent, representing a fresh suppl y from the interior of the earth water bodies = the oceans act as huge reservoir of carbon dioxide, when the atmosphere is slightl y short of the carbon dioxide, the dissolved carbon dioxide changes into gaseous form and return into the atmosphere b) Nitrogen cycle : it is the important constituent of proteins which form an important part in the protoplasm of living organism : onl y green plants can absorb nitrogen in form of nitrates in soil to form proteins, the continuous withdrawal of nitrates by the green plants does not lead to the deficiency of nitrates in soil because of the cycle flow of nitrogen among living organisms and their surroundings (air and soil) Fig. 39 The nitrogen cycle. UB p391 fig 27.5 Forms of nitrogen present in soil inorganic compounds = e.g. nitrates and nitrites of potassium and calcium, ammonia and ammonium compounds organic compounds = e.g. proteins in dead organisms and nitrogenous wastes i.e. urea free nitrogen = the nitrogen gas in the soil air 1. Nitrogen is taken away from soil by i. nitrate is absorbed b y plants and chemos ynthetic bacteria for protein synthesis Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 61 ii. denitrification : denitrifying bacteria decompose nitrate in badl y aerated soil e.g. water-logged soil i.e. nitrates → nitrites + ammonia + nitrogen gas 2. Return of nitrogen to the soil b y i. ammonification : proteins of dead organisms and nitrogenous wastes of animals are decomposed by putrefying bacteria (anaerobic) to form ammonia and ammonium compounds ii. nitrification : the ammonia or ammonium compound are oxidized into nitrites by nitrite bacteria, Nitrosomonas, and then into nitrates by nitrate bacteria, Nitrobacter, in the presence of oxygen (nitrite and nitrate bacteria are collectivel y called nitrifying bacteria) iii. lightning : the strong heating produced during lightning causes some nitrogen combine with oxygen which then dissolved in rain to form nitric acid and are further converted into nitrates in soil iv. industrial method : nitrogen combines with h ydrogen to form ammonia which is used to manufacture artificial fertilizers such as ammonia sulphate 3. Nitrogen fixation by nitrogen fixing bacteria i. free-living nitrogen fixing bacteria, Azotobacter, in the soil is able to absorb nitrogen from soil air and turn it into amino acids which are then turned into proteins in their bodies, when they die, the proteins will be converted into nitrates by the processes of ammonification and nitrification ii. s ymbiotic nitrogen fixing bacteria, Rhizobium, in the root nodules of leguminous plants are able to convert atmosphere nitrogen into amino acids which are then built up into their proteins and some are transported to the leguminous plants, when the bodies of the nitrogen-fixing bacteria decay, their amino acids changed to nitrates by ammonification and nitrification. Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 62 Interdependence of organisms A. Predation : - predation is a t ype of biological interaction in which one species (the predator) attacks and kills another species (the prey). - usuall y the predator populations is much smaller than the prey population otherwise they may not have sufficient food to support them - predator-prey relationships are important in producing cyclic changes in the size of a population (refer to page 38 of the note of this topic) - the t ype of cyclic fluctuation plays an important role in evolution whereby onl y those individuals who are able to escape predation, or withstand adverse climate conditions, will survive to reproduce, the population thereby evolves to be better adapted to the prevailing conditions B. Competition : - when two t ypes of organisms live together in the same habitat, they require the same materials from the environment, their presence strongl y affect one another, this relationship is called competition - there are two t ypes of competition : intraspecific and interspecific competition (refer to page 4 of the note of this topic) -for plants, they compete for sunlight, water, minerals salts and growing spaces - for animals, they may compete for food, shelters and mates C. Symbiosis : - is a mode of life in which two organisms of different species live in intimate association with each other, depending on the nature of the association, the relationship is designated as commensalism, mutualism and parasitism I. Commensalism : - when two t ypes of organisms live together, onl y one organism gains benefit, but the other neither harmed nor benefited, such association is called commensalism • usuall y such association is not permanent and no physical connection is involved • the commensals usuall y gain the benefits of feeding arrangement, protection (shelter) and support • examples 1. the sea anemones live on the shells of the hermit crabs : the sea anemones as sessile animals gain the benefits of moving to a new environment with better food suppl y and obtaining the food remains dropped b y the crabs : the crab also gains some protection from the anemone’s stinging cells and some form of camouflage *since these benefits are not essential and their association is not permanent, it is regarded as commensalism 2. some barnacles attach on the shells of crabs : these sessile commensalism gain the benefits of locomotion and feed on the food remains of the host 3. epiphytes, plants growing on surfaces of the other plants : they grow on the tree trunks to gain support in order to receive more light, they do not draw nutrients from the host plants, they can also easil y absorb water from the bark and from the atmosphere Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 63 II. Mutualism : - when two t ypes of organisms live together and both gain benefits from one another, such association is called mutualism - this association is usuall y a permanent one and in the absence of the other one, they do not live as successful as before or may even die - examples 1. lichens (10% green algae and 90% fungi) : the fungal hyphae entirel y enclose the algal cells to protect them against desiccation, to anchor the plant body on the substratum and to absorb water and mineral salts : the algal cells carry out photos ynthesis to suppl y food to the fungus 2. leguminous plants and nitrogen-fixing bacteria : the nitrogen-fixing bacteria (Rhizobium) living in the root nodules of leguminous plants and change the nitrogen gas into nitrates, the nitrate will be used b y the leguminous plants to produce proteins : the leguminous plants in turn protect the bacteria and suppl y carboh ydrates to support the growth of nitrogen-fixing bacteria 3. cellulase producing bacteria and herbivores : the cellulase-producing bacteria living inside the alimentary canal of the herbivorous mammals (cow, sheep or rabbit) to gain shelter, protection and food suppl y : the herbivores obtain cellulase from these bacteria to digest the cellulase of the plant tissues into sugars Exercise : (97 I 3) The following photograph shows the root morphology of a normal leguminous plant : (a) Identify structure Y. What causes its formation ? [1½ marks] (b) Describe the biological association inside Y and its significance [4 marks] Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 64 III Parasitism : - it is a t ype of close association between two organisms in which one, the parasites, depending upon the other (the host) for the suppl y of nutrients - usuall y the parasites gain benefits from the host and imposes harm to it - examples 1. endoparasites : they live inside the host’s body, usuall y in their guts or tissue fluid e.g. tapeworm is an animal parasite living inside the intestine of man 2. ectoparasites : they live on the bod y surface of their hosts and obtaining their food b y piercing through the outer tissues of the hosts to suck up their body fluids e.g. Dodder is a plant parasite living on clover plants Succession It is a gradual, orderl y and predictable changes in the composition of communities towards a climax communit y Serial stages : is the sequence of communities occurring in each stage of the succession Dominant species : is the t ype of species that make up most of a serial stage Climax communit y : is the final t ype of communit y, it is often described as having one dominant or several co-dominant species Dominance species : normall y refers to those species with the greatest collective biomass or productivit y A. Primary succession : If succession begins on an area which has not been previousl y occupied by communit y (such as newl y exposed rock or sand surface), the process is term as primary succession Fig. 40 Vegetational change during succession BS I 3 r d ed. p320 fig 10.17 Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 65 1. Pioneer plants :- it is the first plants that invade an area and start the series of succession - for bare rocks the plants that can grow on them are the lichens, these plants create a layer of soil on the rock surface by the following routes • as they cling to the rocks, they hold the water on the surface, chemicals such as CO 2 dissolve in the water and corrode the rocks to soil particles • the rock is also split physicall y by their rhizoids • the dead bodies of the lichens enrich the soil with organic matters 2. Moss stage :- after the mosses have established, they compete with lichens and graduall y eliminate the lichens at the area - the mosses continue to build up deposits of organic matter and soil as more rock is broken down and as the old mosses die 3. Herb stage :- some herbs such as the grass may compete with the mosses when an area has been covered with mosses - the herbs finall y eliminate the mosses and become dominant 4. Shrub stage :- the herbs further enrich the soil and they also furnish shade and act as a windbreak, then the soil has more moisture for the growth of the shrubs - as the shrubs grow taller, they become the dominant plants and shade the herbs, i.e. some of the herbaceous plants will not be able to survive 5. Tree stage (forest) :- the next t ype of plants following the shrubs are the trees, as they grow, they will graduall y form a dense vegetation (a forest) that shade out the shrubs, at this stage a climax communit y is said to be reaches - it will remain at equilibrium so far if the environment does not change B. Secondary succession : If succession proceeds in an area where a communit y has been removed (such as a ploughed field or cut forest or fire) the process is called secondar y succession. Secondary succession is usuall y more rapid because the soil has alread y been made receptive by the previous communities. The speed of succession varies greatl y from one situation to another, and the climatic conditions play an important role in determining the speed. Below shows the possible sequence of succession in Hong Kong Bare ground Grassland frequent fire ----→ ----→ maintain grassland Shrub land occasional fires repeated cutting ----→ ----→ ----→ ----→ maintain shrub land diverted to fern community Shrub land with pines repeated cutting ----→ ----→ diverted to pine and fern Pine forest with shrubs Semi-deciduous hardwood forest C. Succession of animals : Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 66 The succession of animals is less defines than plants, and the appearance of species usuall y does not wipe out the existing species [1] At the moss stage, some insects and small invertebrates may be attracted and make their shelter there. [2] At the herbs stage, there will be more insects, especially the grasshoppers, beetles, bees and ants. Attracted by the insects are the insectivorous mammals, e.g. moles and shrews. [3] At the shrub stage, larger mammals make their appearance; these include deer, foxed, rabbits etc. Birds also come here to seek out insects and fruits. [4] At tree stage (climax), the area has similar fauna (animal species) as found in the shrub stage Exercise : (90 I 7c) Distinguish between succession and zonation [2 marks] Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 67 Suggested solution to the Exercise (96 I 1) (a) RTPSQ [1] <<wrong sequence, no mark>> (b) X = Phage DNA [ ½] Y = Bacterial DNA / chromosome [ ½] Events : the tail sheath contracts [ ½] the phage ejects its DNA into the bacterial / host cell [1] (c) Bacterial DNA / chromosome begins to break down [ ½]. Phage DNA replicates [ ½] at the expense of the material of the host cell [ ½]. (90 I 1) Disease cholera malaria measles syphilis rabies influenza Group bacteria protozoa virus bacteria virus virus athlete's foot fungus <<Accept taxonomic grouping at any level, ½ mark each>> hepatitis virus [4] (97 I 1b is also being classified into topic 'Nutrition') Saprophytic mould <any 2 of the following, 1 mark each, accept correct alternative> - rhizoids for penetration into substrate, secretes enzymes for digestion of the substrate / large surface area for absorption of digested food. - sporangia elevated into the air to enhance dispersal of spores - ramifying mycelium to colonize the substrate (97 I 1a) - flattened thallus provides increased surface area for photosynthesis [1] - holdfast to attach to a substratum for prevention of being washed away by wave [1] - leathery (tough) or flexible body resists action of waves [1] - air-bladders keep the alga buoyant for capturing light for photosynthesis [1] - mucilage conserves water when alga is exposed to dry conditions [1] any 2 (99 I 1) (a) Sporangium [1], produce spores [1/2], formation of gameophyte [1/2]/ propagation / reproduction of the species, and disperse the spore [1/2] (b) diploid [1/2] / 2n / 2 (94 I 1) Mosses : found in damp / moist habitat, shady and cool environment [½] Ferns : found in open areas, near to hillside / roadside / on walls, where moisture is available for certain time of the year (for fertilisation) [½] Features : (1 for each feature mentioned, 2 marks max. for moss and 2 marks max. for fern) Water conservation / uptake Reproduction Mosses Ferns i. no cuticle water and nutrients diffuse i. have woolly (hairy) cuticle so can reduce water loss rapidly in and out, restricted to grow in moist habitat ii. no true roots only rhizoid, water uptake is ii. true roots to facilitate water uptake so can stand drier areas less efficient so restricted to moist habitat iii. grow tightly together in form of a mat for water retention both male gametes are mobile, so necessity for water medium to complete its life cycle Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 68 (98 I 1) <<accept alternatives other than those listed below that are group characteristics only, deduct ½ mark for no tabulation>> (a) (b) Group Echinodermata Cnidaria Features - pentaramous symmetry [1] - tube-feet [1] - calcareous scales / spines on body [1] - body with oral and aboral surfaces [1] - radial symmetry [1] - possesses tentacles [1] - single body opening [1] any 2 any 2 (93 II 5) Compare and contrast body organization : Hydroid coelenterate diploblastic : jellyfish like mesoglea sandwiched between ectoderm and endoderm tissue-level organisation acoelomate Tapeworm muticellular animals triploblastic : endoderm, organ-level organisation (many organs reduced) acoelomate (continuous proliferation of proglottids) not metamerically segmented radially symmetrical Earthworm mark 1 mesoderm, ectoderm 1 organ-level organisation 1 coelomate 1 metamerically segmented bilaterally symmetrical 1 1 Significance of the differences : Diploblastic VS triploblastic : the mesoderm has given triploblasts (tapeworm, earthworm) a greater bulk of cellular material [½] compared with their volume, than that found in diploblasts (e.g. Hydra), causing wide separation of digestive tube from body wall [½] and hence lead to problems of transport of oxygen, excretory products and food [½]. In tapeworm (triploblastic acoelomate) the problem of oxygen supply is solved by restriction of the body to small volume and flattened shape [½]. For excretion, a flame-cell system [½] with ducts opening on the surface, is developed in the mesoderm [½]. The new mass of mesoderm is utilised in the formation of new tissues and organs [½] e.g. muscular tissue, excretory system, reproductive system [½]. Tissue-level organisation VS organ-level organisation : the tissue level of organization occurs in Hydra. [½] Cells are grouped in coherent masses for performance of one or more special functions [½] e.g. musculo-epithelial tissue, nervous tissue. The tentacles may be given the status of organs, [½] consisting of several types of tissues (musculo-epithelial cells, sensory cells, interstitial cells, nematoblasts, endoderm cells) co-ordinated for performance of one or more functions (food capture, conveyance of food to mouth, looping movements). [½] Division of labours among cells [½] lead to formation of organs [½]. Specialised for more sophisticated functions in tapeworm and earthworm e.g. ovary and testis in tapeworm, nephridia in earthworm. [½] In tapeworm, in adaptation to its parasitic mode of life, [½] there is no alimentary canal. [½] Digested food of the host is absorbed over whole surface. [½] The nervous system is reduced. [½] A very large number of proglottides are produced. [½] The oldest proglottis is the most posterior. Every mature proglottis contains a full set of male female reproductive organs. [½] <<max. 4 marks>> Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 69 Acoelomate VS coelomate : movements of body wall occur independently of peristaltic movements of gut wall and digestive processed. [½] The coelom provides a large cavity [½] in which organs can be developed [½] and can perform their functions without interference from other organs [½]. Location of these organs in coelom necessitates excretory and reproductive ducts [½] to convey products to exterior. [½] Coelomic fluid gives support, protection and assistance with locomotion. [½] Development of coelom has necessitated a blood-vascular system for transport of digested food and oxygen. [½] Proglottis VS metamerism : the earthworm exhibits metameric segmentation. [½] Typically every segment is exactly similar. [½] Although the segments are partitioned from one another, they are co-ordinated and do not function as independent units. [½] The main advantage of segmentation is that it provides an opportunity for specialisation in certain segments. [½] The oldest segment is the most anterior. [½] The continuous proliferation of proglottids in tapeworm enhances the animals chance of survival due to production of large numbers of eggs [½]. << max. 2 marks>> Radial symmetry VS bilateral symmetry : any appropriate significance in relation to body symmetry. e.g. radial symmetry in relation to the sessile life of some coelenterates. [2] <<Max. 20 marks>> (96 I 3) Planarian do not have coelom [½], no metamerism. [½] In earthworms : mesoderm splits into outer and inner layer [ ½] with coelom in between [ ½] which allows for : - space for development of organs [ ½] - development of hydrostatic skeleton for support and / or movement [1] - independent movement of body wall and gut [1] metameric segmentation [ ½] allows for : specialization of different body parts / division of labour / muscular body wall divides into blocks provides for independent movement of different parts of the body. [1] << max. 5 >> (99 I 5) Group Function <any 1, 1 @> - maintains body shape / support Annelida, Annelid(s) [1] - muscles of body wall acts on coelomic fluid to bring about locomotion (b) - catching / kill / trap preys Cnidaria / Cnidarian/ Coelenterata / <not accept ‘feeding’> Coelenterate(s) [1] - defense (a) <deduct ½ mark if no tabulation> (97 I 8) (a) L : 1A, 2A [1] Psettodes erumei [ ½] M : 1A, 2B, 3A, 4A [1] Pseudorhombus arsius [ ½] N : 1B, 6B [1] Cynolgossus abbreviatus [ ½] (b) - eyes located on one side to allow for vision while swimming on the ocean floor [1] - dorsal and ventral fins are elongated used to swim near the bottom [1] / used to move sand / mud and bury in the bottom, - flat body makes it possible to lie flat on the ocean floor / flat body makes it inconspicuous on the ocean floor. [1] << any 2 points>> Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 70 (90 I 7a) Habitat is the place in nature [1/2] where the species lives (or where you can find the species) [1/2] Niche is the functional role of the species [1/2] i.e. what it does in the community, including the habitat, food, nest sites, its place in the community in relation to other species and so on, that it needs in order to survive. [1/2] (93 I 6b) A biome is an ecological term used to describe a major terrestrial community unit which results from an interaction between regional climate and biota. [1] A habitat is an ecological concept of a space which is characterized by a set of physical conditions or limiting factors that influence the presence, distribution and survival of organisms within it. [1] (99 I 4) (a) predator-prey relationship [1] / X preys on Y / predation (b) (i) at least 2 oscillation cycles are shown [1/2], Y and X out of phase [1/2], peak for Y higher than that of X [1/2], 2 curves correctly labeled as X and Y [1/2] <axes without labels – ½> no of individuals Y X Time (ii) Both X and Y would not die out complete [1]. In the natural environment, as the population density of Y falls, it would be difficult for X to locate Y [1]. When X falls in population, Y will take chance to proliferate [1/2] and this is followed by an increase in X population as more food is available. (91 II 4b-d) A named local habitat e.g. mangrove (a) The two physical factors described must be major ones operating at the specified habitat e.g. the salinity and the anaerobic soil in mangrove [1] Correctly state the effects of the factors on distribution [ ½ x 3 x 2] (b) The organisms named must be present in the habitat, adaptations cited must be adaptations towards the particular habitat specified, general adaptations not acceptable. For each organism : - correct name (common name acceptable) [1/2] - at least two adaptations [ ½ x 2] Total : 1.5 x 4 (c) The examples cited must be present in the habitat for each inter-relationship : - correct examples (both partners correct) [ ½ x 2 x 2] - description of the role of each partner [ ½ x 2 x 2] Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 71 (91 II 4a) A named local habitat e.g. mangrove (a) Use transects [1/2] and quadrats [1/2] to measure the abundance and distribution of species. [1/2] e.g. Line transect • select a typical stretch of areas of interest in the habitat [1/2] • laid a rope in ground (fixed at the 2 ends) [1/2] • record abundance and distribution of species touching the rope [1/2] • data graphed (histograms / kite diagrams ) and analyzed [1/2] e.g. quadrats • random or along a line transect (belt transect) [1/2] • count the number of each species occurring in the quadrat [1/2] / estimate the percentage coverage of each species in the quadrat [1/2] • for random quadrat : repeat a number of times to get the average [1/2] • for belt transect : repeat along the transect [1/2] (90 I 7b) Biomass is the amount of living material [1/2] ( e.g. in terms of weight or carbon) of a biological unit at any given time. [1/2] Production is the difference in biomass [1/2] within a certain time interval. [1/2] i.e. final biomass initial biomass. (98 I 11) (a) (i) X : (950) / (11360) x 100 % [1/2] = 8.36 % [1/2] Y : (8750) / (9250) x 100 % [1/2] = 94.59 % [1/2] (ii) X : coniferous [1/2] Y : deciduous [1/2] (b) Yes [1/2]. All growth stages of A are present [1/2] in forest X[1/2] but not in Y. Absence of seedlings and saplings in Y [1/2] indicates that fire may be essential for the initial growth phase of A [1/2]. A becomes the dominant species (component) of the forest tree community in X where fire is periodic but not in Y [1]. In X, species A is mostly represented by mature trees [1/2], prolific number of seedlings in X perpetuates the species [1/2] / indicating that growth is not interrupted. <max. 4> < Bonus : The periodic burning away of deciduous trees by fires in X removed the competitor of A [1]> (c) B only exists in X but not in Y [1/2]. Without fire, the luxurious growth of deciduous trees in forest Y outcompeted species B [1]. / The cones of B need fire to split open to release the seeds. / Fire exposes the bare grounds for the germination of the seeds of B. (d) Fire is destructive to / limits the growth of deciduous trees [1/2] because in forest X, where fires occurred periodically, the total number of deciduous trees is much reduced [1/2]. The seedlings and saplings which form the under-growth were burnt by the low-level fires which occurred every 5 years [1]. Thus only a few survived to reach maturity [1/2]. Compared to forest Y where fire is absent, deciduous trees become dominant [1/2]. Fire also shifted the dominant tree species from C to D in X [1/2] because in Y the more dominant species in C [1/2] <Bonus : probably C is more sensitive to fire / D is more fire tolerant [1/2]> Buddhist Chi Hong Chi Lam Memorial College A.L. Bio. Notes (by Denise Wong) Variety of Life and Relation of Organisms with their Environment ...... Page 72 (e) Allow the regular fires to occur periodically [1/2]. Fire proved to promote species diversity [1], at least conifer trees can't survive well without fires [1/2]. / Conifer trees grow luxuriously because fire reduced the competition from deciduous trees. Fire also cleared off the ground and add ash to the soil thus increased soil fertility [1]. (97 I 3) In the pyramid of energy, there is a progressive decrease in energy flowing through successive trophic levels up a food chain [1/2]. This is due to a net loss of energy to the environment [1/2] as a result of processes such as <any 2> respiration / heat loss / dead body wastage / incomplete eating [1/2]. Inverted pyramids of biomass can result when the turn-over rate (high reproductive rate) of producers is fast compared to the consumers [1], thus at any time the standing biomass of the producer can be smaller [1/2] to sustain a larger biomass of consumers [1/2]. (90 I 7c) Zonation refers to the spatial distribution pattern of various species [1/2] within a community at any one time according to the environmental gradient. [1/2] Succession refers to the replacement of some species within a community by other species [1/2] through time. [1/2]