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 ecosystem comprises biotic and abiotic components which interact extensively with each other. Based on their ecological roles, the biotic components of an ecosystem can be classified as : Producer : they are the green plants which absorb solar energy to synthesize complex organic compounds from simple inorganic substances by photosynthesis, they act as the ultimate food source to all the heterotrophs : other producers are green algae and blue green algae, they are mainly 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 mainly 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 primary 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 mainly bacteria, fungi and some flagellates : by means of their saprophytic activities, they decompose the eliminated products of animals and the dead bodies of the organisms into simple compounds : these compounds are absorbed as nutrients by the green plants again : they enable the nutrients to be used continuously in a cyclic form in the ecosystem : 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 rapidly Energy and essential materials are therefore transferred from producers to consumers through the feeding processes. Eventually, decomposers break down the organic matter and release inorganic materials back to the environment. These inorganic materiasl are used by 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
Primary secondary Tertiary Ecosystem Producer consumer consumer consumer freshwater pond green algae → protozoa → mosquito larva → fish rocky pond sea weeds → molluscs → starfish → sea birds Grassland grass → grasshopper → lizard → snake Woodland green plants → caterpillars → sparrow → 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 ecosystem 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 community : 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 3rd ed. p300 fig 10.2
Fig. 35 A simple schematic comparison of terrestrial and aquatic ecosystems
Energy flow in the ecosystem I. Productivity : Refers to the amount of energy or living materials fixed in a population, or a trophic level, or an entire ecosystem in a given time a) gross primary productivity : rate of dry matter production by photosynthesis in an ecosystem, it does not represent the actual amount of food potentially 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 productivity : it is the biomass which is incorporated into a plant community during a specific time intervals, minus the part respired c) secondary productivity : 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, only small parts can be used in photosynthesis
Energy Dissipation Percent / % Reflected 30 Direct conversion to heat 46 Evaporation, precipitation (drives hydrological 23 cycle) Wind, waves and currents 0.2 Photosynthesis 0.8 Total 100
BSI 3rd ed. p302 fig10.4
Fig. 36 Flow of energy and cycling of materials through a typical food chain.
• the energy supplies for the grass, only a small part is used in the synthesis of organic materials, much are lost • part of the primary productivity is used in the respiration of the producers, of the net primary productivity, a portion is eaten by the primary consumers, the rest remains unused and is passed as dead plant materials • of the food eaten by 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 pyramids : The feeding relationships between organisms at different trophic level within a community can be represented by ecological pyramids. The producers (green plants) form the base of the pyramids 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) Pyramid 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 usually smaller than that of the one they are feeding on thus can be expressed in the form of a pyramid, 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 th trophic level
3 rd trophic level
2 nd trophic level
1 st trophic level
Examples : Normal A tree is the A tree which is Grasses are pyramid producer, on infested with eaten by a cow which worms parasites and which is are the lived, the latter are infested with that are eaten parasitized by parasites. by birds. further parasites.
b) Pyramid of biomass : the graphical representation of the trophic structure for a community 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.
BSI 3rd 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 pyramids 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 pyramids of biomass is found in open water and deep water ecosystem 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) Pyramid of energy : at each transfer of energy from one trophic level to the next higher, there is always a loss of energy from the system : 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 difficulty 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 (productivity) : it permits comparison of trophic structure of different ecosystem 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 pyramid 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 ecosystem and be recycled again to be available to producers, e.g. the flow of energy in an ecosystem is unidirectional while that of materials or nutrients is cyclic. The importance of decomposers in an ecosystem 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 photosynthesis and fix it as carbohydrates and later into other organic compounds animals = they feed on plants, removes the carbon dioxide indirectly fossil fuels = millions of years ago, the dead remains of organisms in soil or compressed under water slowly 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 system water bodies = carbon dioxide dissolves readily 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 by 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 continuously emitted from volcanic vent, representing a fresh supply from the interior of the earth water bodies = the oceans act as huge reservoir of carbon dioxide, when the atmosphere is slightly 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 : only 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 by plants and chemosynthetic 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 badly aerated soil e.g. water-logged soil i.e. nitrates → nitrites + ammonia + nitrogen gas 2. Return of nitrogen to the soil by 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 collectively 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 hydrogen 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. symbiotic 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 type of biological interaction in which one species (the predator) attacks and kills another species (the prey). - usually 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 type of cyclic fluctuation plays an important role in evolution whereby only 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 types of organisms live together in the same habitat, they require the same materials from the environment, their presence strongly affect one another, this relationship is called competition - there are two types 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 types of organisms live together, only one organism gains benefit, but the other neither harmed nor benefited, such association is called commensalism • usually such association is not permanent and no physical connection is involved • the commensals usually 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 supply and obtaining the food remains dropped by 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 easily 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 types of organisms live together and both gain benefits from one another, such association is called mutualism - this association is usually 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 entirely 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 photosynthesis to supply 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 by the leguminous plants to produce proteins : the leguminous plants in turn protect the bacteria and supply carbohydrates 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 supply : 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 type of close association between two organisms in which one, the parasites, depending upon the other (the host) for the supply of nutrients - usually the parasites gain benefits from the host and imposes harm to it - examples 1. endoparasites : they live inside the host’s body, usually 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 body surface of their hosts and obtaining their food by 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, orderly and predictable changes in the composition of communities towards a climax community Serial stages : is the sequence of communities occurring in each stage of the succession Dominant species : is the type of species that make up most of a serial stage Climax community : is the final type of community, it is often described as having one dominant or several co-dominant species Dominance species : normally refers to those species with the greatest collective biomass or productivity A. Primary succession : If succession begins on an area which has not been previously occupied by community (such as newly exposed rock or sand surface), the process is term as primary succession Fig. 40 Vegetational change during succession
BSI 3rd 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 CO2 dissolve in the water and corrode the rocks to soil particles • the rock is also split physically 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 gradually 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 finally 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 type of plants following the shrubs are the trees, as they grow, they will gradually form a dense vegetation (a forest) that shade out the shrubs, at this stage a climax community 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 community has been removed (such as a ploughed field or cut forest or fire) the process is called secondary succession. Secondary succession is usually more rapid because the soil has already been made receptive by the previous communities. The speed of succession varies greatly 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 ----→ ----→ maintain shrub land repeated cutting ----→ ----→ 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 usually 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] <
(90 I 1) athlete's Disease cholera malaria measles syphilis rabies influenza hepatitis foot Group bacteria protozoa virus bacteria virus virus fungus virus
<
(97 I 1b is also being classified into topic 'Nutrition') Saprophytic mould
(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] any 2 - air-bladders keep the alga buoyant for capturing light for photosynthesis [1] - mucilage conserves water when alga is exposed to dry conditions [1]
(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)
Mosses Ferns Water conservation i. no cuticle water and nutrients diffuse i. have woolly (hairy) cuticle so can reduce / uptake rapidly in and out, restricted to grow in water loss moist habitat ii. no true roots only rhizoid, water uptake is ii. true roots to facilitate water uptake so can less efficient so restricted to moist habitat stand drier areas iii. grow tightly together in form of a mat for water retention Reproduction 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) <
Group Features (a) Echinodermata - pentaramous symmetry [1] - tube-feet [1] any 2 - calcareous scales / spines on body [1] - body with oral and aboral surfaces [1] (b) Cnidaria - radial symmetry [1] - possesses tentacles [1] any 2 - single body opening [1]
(93 II 5) Compare and contrast body organization :
Hydroid coelenterate Tapeworm Earthworm mark muticellular animals 1 diploblastic : jellyfish like mesoglea sandwiched between triploblastic : endoderm, mesoderm, ectoderm 1 ectoderm and endoderm organ-level tissue-level organ-level organisation 1 organisation organisation (many organs reduced) acoelomate (continuous acoelomate coelomate 1 proliferation of proglottids) metamerically not metamerically segmented 1 segmented radially symmetrical bilaterally symmetrical 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] <
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] <
(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
(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]
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.
(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
(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]