Questions: Organisms and Populations

Q1. List the attributes that a population has but an individual does not.

Answer (English): A population has a birth rate and a death rate, both expressed per capita, while an individual only has a birth and a death. A population also has a sex ratio and an age distribution, which is shown as an age pyramid. Population size, or density, is another population attribute, and it is expressed in numbers, biomass or per cent cover depending on the species.

Hinglish: Population ke paas birth rate aur death rate hote hain, aur dono per capita hote hain; individual ke paas sirf ek birth aur ek death hoti hai. Population ka sex ratio aur age distribution bhi hota hai, jise age pyramid se dikhate hain. Population density bhi population ka attribute hai, aur species ke hisaab se ise numbers, biomass ya per cent cover mein likhte hain.

Q2. If a population growing exponentially doubles in 3 years, what is its intrinsic rate of increase?

Answer (English): For exponential growth, Nt = N0 e^(rt). If the population doubles, Nt/N0 = 2, so 2 = e^(3r). Taking natural logarithms, ln 2 = 3r, so r = 0.693/3, which is about 0.231 per year. The intrinsic rate of natural increase is therefore roughly 0.231 per year.

Hinglish: Exponential growth ka formula Nt = N0 e^(rt) hai. Population double hoti hai to Nt/N0 = 2, yaani 2 = e^(3r). Natural log lene par ln 2 = 3r, isliye r = 0.693/3 ≈ 0.231 per year. Matlab intrinsic rate of natural increase lagbhag 0.231 per year hai.

Q3. Name two kinds of defence that plants use against herbivores.

Answer (English): Two broad kinds exist. Morphological defences include thorns and spines, as in Acacia and cactus. Chemical defences include substances that make the herbivore sick, block feeding or digestion, upset reproduction or kill it. Calotropis produces poisonous cardiac glycosides, and nicotine, caffeine, quinine, strychnine and opium are plant chemicals that originally served as defences against grazers.

Hinglish: Plants do tarah se bachti hain: morphological defence mein thorns aur spines (Acacia, cactus), aur chemical defence mein aise padarth jo herbivore ko bimar karein, khana ya pachna rok dein, reproduction bigaadein ya maar dein. Calotropis cardiac glycosides banata hai; nicotine, caffeine, quinine, strychnine aur opium bhi asal mein grazers ke against defence the.

Q4. An orchid grows on the branch of a mango tree. How would you describe this interaction?

Answer (English): The interaction is commensalism. The orchid gains a place to grow and better access to light, so it benefits, while the mango tree is neither helped nor harmed. In plus-minus-zero notation this is a (+ , 0) interaction.

Hinglish: Yeh commensalism hai. Orchid ko grow karne ki jagah aur roshni ka fayda milta hai, lekin mango tree ko na fayda hota hai na nuksaan. Plus-minus-zero mein yeh (+ , 0) interaction hai.

Q5. What ecological principle is used in biological control of pest insects?

Answer (English): Biological control uses the predator-prey relationship. A predator that naturally regulates a pest population is introduced or encouraged, so the pest is kept down without chemicals. The principle is that predators control prey numbers, which is why an exotic pest that arrives without its natural predators spreads rapidly. The prickly pear cactus in Australia was brought under control by introducing a cactus-feeding moth from its native habitat.

Hinglish: Biological control predator-prey relation par chalta hai. Jo predator naturally pest population ko control karta hai use introduce ya encourage kiya jaata hai, taki bina chemicals ke pest kam rahe. Principle yeh hai ki predators prey numbers ko control karte hain; isi liye exotic pest bina natural predators ke tezi se phailta hai. Australia mein prickly pear cactus ko uske native habitat se cactus-feeding moth laakar control kiya gaya tha.

Q6. Define population and community.

Answer (English): A population is one species' group of individuals in a defined area, sharing or competing for resources, and able to interbreed. A community is the collection of populations of different species living and interacting in the same area, for example all the plants, animals and microbes in a patch of forest.

Hinglish: Population ek hi species ke individuals ka group hai jo ek defined geographical area mein rehta hai, resources share ya compete karta hai aur interbreed kar sakta hai. Community alag-alag species ki populations ka collection hai jo ek hi area mein rehti aur interact karti hai, jaise forest ke ek hisse ke saare plants, animals aur microbes.

Q7. Give a definition and one example for each of these: commensalism, parasitism, camouflage, mutualism and interspecific competition.

Answer (English): Commensalism is a (+ , 0) interaction, for example an orchid on a mango branch. Parasitism is a (+ , -) interaction in which the parasite lives on or in the host, for example Cuscuta on a hedge plant. Camouflage is a defence in which an organism blends with its surroundings, as some insects and frogs do. Mutualism is a (+ , +) interaction, for example lichens or the fig and its wasp. Interspecific competition is a (- , -) interaction between species for the same resource, as between the barnacles Balanus and Chathamalus on rocky coasts.

Hinglish: Commensalism (+ , 0) hai, jaise mango par orchid. Parasitism (+ , -) hai, jismein parasite host par ya uske andar rehta hai, jaise hedge plant par Cuscuta. Camouflage mein organism apne surroundings se mil jaata hai, jaise kuch insects aur frogs. Mutualism (+ , +) hai, jaise lichen ya fig aur uski wasp. Interspecific competition (- , -) same resource ke liye species ke beech hoti hai, jaise rocky coast par Balanus aur Chathamalus barnacles ke beech.

Q8. Describe the logistic population growth curve.

Answer (English): Logistic growth happens when resources are limited. The population first shows a lag phase, then acceleration, then deceleration, and finally levels off at the carrying capacity K, giving a sigmoid curve when N is plotted against time. The equation is dN/dt = rN(K - N)/K, where r is the intrinsic rate of natural increase. Because most habitats have finite resources, the logistic model is more realistic than the exponential one.

Hinglish: Logistic growth tab hoti hai jab resources limited hote hain. Pehle lag phase, phir acceleration, phir deceleration, aur aakhir mein population carrying capacity K par level off ho jaati hai; N ko time ke against plot karne par sigmoid curve milta hai. Equation dN/dt = rN(K-N)/K hai, jahan r intrinsic rate of natural increase hai. Zyadatar habitats mein resources finite hote hain, isliye logistic model exponential se zyada realistic hai.

Q9. Select the statement that best explains parasitism.

Answer (English): The correct statement is that one organism is benefited and the other is affected. The parasite gains food and shelter, while the host loses in survival, growth or reproduction. Options saying that both benefit, or that the other is unaffected, describe mutualism and commensalism instead.

Hinglish: Sahi statement hai ki ek organism ko fayda hota hai aur doosra affected hota hai. Parasite ko khana aur rehne ki jagah milti hai, jabki host ki survival, growth ya reproduction par asar padta hai. Jo options dono ko fayda ya doosre ko unaffected batate hain, woh mutualism aur commensalism hain.

Q10. Name three key features of a population and explain each.

Answer (English): Three important characteristics are population density, birth and death rates, and age distribution. Density is the number of individuals per unit area or volume, though biomass or per cent cover may be used for some species. Birth and death rates are per-capita figures that show how fast a population is adding or losing members. Age distribution is the proportion of individuals in each age group, and its age pyramid indicates whether a population is growing, stable or declining.

Hinglish: Teen important characteristics hain population density, birth aur death rates, aur age distribution. Density per unit area ya volume individuals ki sankhya hai, lekin kuch species ke liye biomass ya per cent cover use karte hain. Birth aur death rates per capita hote hain jo batate hain population kitni tezi se badh ya ghat rahi hai. Age distribution har age group ka proportion hai, aur uski age pyramid batati hai ki population growing, stable ya declining hai.

To check how much of this stuck, take the five-question quiz below. Each answer explains the reasoning, so read the explanation even when you get it right.

Quiz: the five question check for this chapter is set from the same topics. Attempt it after the questions above, then revisit any topic page where you lost a mark.