Majority of flowering plants are pollinated by biotic agents, especially insects.
Why do wind- and water-pollinated plants produce enormous amounts of pollen?
Because pollen reaching the stigma is largely a chance event, resulting in considerable pollen wastage. Therefore, they compensate by producing very large quantities of pollen grains.
2. Wind Pollination — Anemophily
Wind is the most common abiotic agent of pollination.
Adaptations of wind-pollinated flowers
Pollen grains are light
Pollen grains are non-sticky
Stamens are well exposed for easy pollen dispersal
Stigma is large and often feathery to trap airborne pollen
Usually one ovule per ovary
Flowers are often numerous and packed into an inflorescence
Common in grasses
🌽 Example: Maize
The familiar corn cob has long, thread-like structures that are actually stigma and style, which help trap pollen carried by wind.
Water pollination is very rare in flowering plants.
Limited to about 30 genera
Mostly found in monocotyledons
Examples
Vallisneria
Hydrilla
Zostera (seagrass)
Important distinction
Not every aquatic plant is water-pollinated.
For example:
Water hyacinth
Water lily
Their flowers emerge above the water surface and are pollinated by insects or wind.
Vallisneria
Female flowers reach the water surface through a long stalk.
Male flowers/pollen grains are released onto the water surface.
Pollen is carried passively by water currents.
Eventually, pollen reaches the stigma of the female flower.
Seagrasses — Zostera
Female flowers remain submerged.
Pollen grains are released underwater.
Pollen grains are often long and ribbon-like.
They are carried passively by water currents.
In many water-pollinated species, pollen grains have a mucilaginous covering that protects them from wetting.
Why are wind- and water-pollinated flowers usually not colourful and nectar-producing?
Because they do not need to attract animals.
Therefore, they generally:
are not brightly coloured
do not produce nectar
often lack fragrance
These features are important for animal-pollinated flowers, not for wind/water pollination.
4. Animal Pollination — Zoophily
Majority of flowering plants use animals as pollinating agents.
Common pollinators
🐝 Bees
🦋 Butterflies
🪰 Flies
🪲 Beetles
Wasps
Ants
Moths
Birds
Bats
Insects, particularly bees, are the dominant biotic pollinating agents.
Even some:
Primates such as lemurs
Tree-dwelling rodents
Reptiles such as geckos and garden lizards
can act as pollinators.
Adaptations of animal-pollinated flowers
Most insect-pollinated flowers are:
Large
Colourful
Fragrant
Rich in nectar
If flowers are small, many flowers are grouped into an inflorescence to make them conspicuous.
Attraction
Animals are attracted by:
Colour
Fragrance
Special example
Flowers pollinated by flies and beetles may produce foul odours to attract them.
Floral Rewards
Flowers provide rewards to encourage repeated animal visits.
Main rewards:
Nectar
Pollen grains
During feeding, the animal comes into contact with: Anther → pollen sticks to animal body → animal visits another flower → pollen reaches stigma
Pollen of animal-pollinated flowers is generally sticky.
Special Pollination Relationships
Amorphophallus
Some flowers provide animals with a safe place to lay eggs as a floral reward.
Yucca and moth
A highly specific relationship exists between Yucca plant and a particular moth.
Moth lays eggs in the ovary.
Moth simultaneously pollinates the flower.
Developing seeds provide food for the moth larvae.
Both organisms depend on each other to complete their life cycles.
Pollen/Nectar Robbers
Not every flower visitor is a pollinator.
Some insects may take:
pollen
nectar
without coming into contact with the anther and stigma.
Such visitors are called:
Pollen/nectar robbers
5. Outbreeding Devices
Why are outbreeding devices needed?
Most flowering plants have bisexual/hermaphrodite flowers.
Therefore, pollen can easily reach the stigma of the same flower.
Continuous self-pollination can cause:
Inbreeding depression
Hence, flowering plants have evolved mechanisms to discourage self-pollination and promote cross-pollination.
Important Outbreeding Devices
1. Dichogamy
Pollen release and stigma receptivity are not synchronised.
Two possibilities:
Protandry: Anthers release pollen before stigma becomes receptive.
Protogyny: Stigma becomes receptive before pollen is released.
Both prevent autogamy.
2. Herkogamy
Anther and stigma are positioned at different locations within the flower.
Therefore, pollen cannot easily reach the stigma of the same flower.
Prevents autogamy.
3. Self-incompatibility
A genetic mechanism that prevents self-pollen from fertilising the ovules.
It may inhibit:
Pollen germination, or
Pollen tube growth
Self-incompatibility prevents both self-pollination-related fertilisation from the same flower and, depending on the system, pollen from other flowers of the same plant.
4. Unisexual Flowers
Monoecious condition
Male and female flowers occur on the same plant.
Examples:
Castor
Maize
This prevents:
❌ Autogamy
But does not prevent:
Geitonogamy
Dioecious condition
Male and female flowers occur on different plants.
Example:
Papaya
This prevents:
❌ Autogamy ❌ Geitonogamy
⭐ Papaya → dioecious → both autogamy and geitonogamy prevented
Pollen–Pistil Interaction
Pollination does not guarantee fertilisation.
Why?
Because the pollen landing on the stigma may be:
Compatible → accepted
Incompatible → rejected
Pistil recognition
The pistil recognises whether pollen is of the correct type through a chemical interaction between pollen and pistil components.
Compatible pollen
Pistil accepts it → pollen germinates → pollen tube develops.
Pollination = Transfer of pollen grains from the anther to the stigma of a pistil.
Since male and female gametes are non-motile, pollination brings them together for fertilisation.
2. Agents of Pollination
External agents include:
🌬️ Wind — Anemophily
🐝 Insects — Entomophily
🐦 Birds — Ornithophily
🦇 Bats — Chiropterophily
💧 Water — Hydrophily
3. Types of Pollination
Type
Transfer of pollen
Genetic nature
Autogamy
Anther → stigma of the same flower
Similar to self-pollination
Geitonogamy
Anther of one flower → stigma of another flower on the same plant
Genetically similar to autogamy
Xenogamy
Anther of one plant → stigma of a different plant
Genetically different
Autogamy
Occurs within the same flower.
Requires:
Synchrony between pollen release and stigma receptivity
Anther and stigma should be close together
Complete autogamy is relatively rare in normal open flowers.
Cleistogamy
Cleistogamous flowers do not open.
Examples:
Viola
Oxalis
Commelina
Because anthers and stigma are very close, pollen reaches the stigma within the unopened flower.
Key point:
Cleistogamous flowers are invariably autogamous and provide assured seed set even without pollinators.
Advantage: Reproduction is assured even when pollinators are absent. Disadvantage: It does not promote genetic variation because cross-pollination is prevented.
Geitonogamy
Pollen transfer occurs between two different flowers of the same plant.
Functionally → cross-pollination, because a pollinating agent is generally required.
Genetically → similar to autogamy, because pollen and ovule originate from the same plant.
Xenogamy
Pollen is transferred from one plant to the stigma of a different plant of the same species.
Most important: Xenogamy is the only type that brings genetically different pollen grains to the stigma.
🔥 NEET One-Liners
Same flower → Autogamy
Different flowers, same plant → Geitonogamy
Different plants → Xenogamy
Cleistogamous flowers → Always autogamous
Genetically different pollen → Xenogamy
Assured seed set without pollinators → Cleistogamy
A population is a group of individuals of the same species living in a well-defined geographical area, sharing resources and potentially interbreeding.
Examples:
Cormorants in a wetland
Rats in an abandoned house
Teak trees in a forest
Bacteria in a culture plate
Lotus plants in a pond
Important: Even organisms reproducing asexually can be considered a population in ecological studies.
2. Population Ecology
Population ecology connects: Ecology ↔ Population Genetics ↔ Evolution
Natural selection operates at the population level, although individual organisms experience environmental changes.
3. Population Attributes
An individual organism does not have population attributes, but a population does.
Population Attribute
Meaning
Birth rate (Natality)
Rate of addition of new individuals
Death rate (Mortality)
Rate of loss of individuals
Sex ratio
Proportion of males and females
Age distribution
Distribution of individuals among different age groups
Population density (N)
Number/measure of individuals in a given area or volume
4. Birth Rate
So, birth rate = 0.4 offspring per lotus per year.
5. Death Rate
6. Sex Ratio
It represents the proportion of males and females in a population.
Example:
60% females + 40% males
An individual is either male or female, but a population has a sex ratio.
7. Age Distribution & Age Pyramid
A population contains individuals of different ages.
The graphical representation of the age distribution is called an age pyramid.
The shape indicates whether the population is:
(a) Expanding / Growing
➡️ Large proportion of pre-reproductive individuals
(b) Stable
➡️ Relatively similar proportion of pre-reproductive and reproductive groups
(c) Declining
➡️ Smaller proportion of pre-reproductive individuals
NEET point: Age pyramid reflects the growth status of a population.
8. Population Size / Population Density
Population size is technically called population density, represented by:N
It is not always expressed simply as the total number of organisms.
Different ways to measure population density:
1. Number
Appropriate when individuals can be counted easily.
2. Biomass
Useful when organisms differ greatly in size.
3. Percentage cover
Useful for plants with large canopies.
4. Relative density
Used when absolute counting is difficult.
Examples
Banyan vs Parthenium:
Suppose:
Parthenium = 200 plants
Banyan = 1 large tree
Simply saying banyan has a lower density based on number can be misleading because one banyan may occupy a huge area and have a major ecological role.
Therefore, percentage cover or biomass may be more meaningful.
Bacteria in a Petri Dish
When bacterial population is extremely large and direct counting is difficult, biomass or other indirect measures can be used.
Fish Population
Instead of counting every fish in a lake:
Number of fish caught per trap
can be used as a measure of relative density.
9. Population Density May Be Estimated Indirectly
In many cases, organisms are not actually counted or directly observed.
Tiger Census
Tiger population is often estimated using indirect evidence such as:
Pug marks
Fecal pellets
Thus, population size can be estimated indirectly.
NEET/JEE One-Liners
Population density is represented by → N
Population has birth rate and death rate; individual has births and deaths.
Sex ratio is a population attribute.
Age pyramid represents → age distribution of a population.
Age pyramid indicates → growth status of population.
Growing population → more pre-reproductive individuals.
Population density need not always be measured by number.
Biomass/percentage cover can be used to estimate population density.
Fish caught per trap → relative density.
Tiger census → indirect estimation using pug marks and fecal pellets.
Population ecology links ecology with population genetics and evolution.
Natural selection operates at the population level.
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Topic: Group 13 — B, Al, Ga, In, Tl Level: JEE Main + NEET | PYQ-pattern Type: Single correct answer
Questions
1. The element of Group 13 having the highest first ionisation enthalpy is:
A. B B. Al C. Ga D. Tl
2. Which of the following is the most stable oxidation state of thallium?
A. +3 B. +2 C. +1 D. +5
3. The correct order of atomic radii of Group 13 elements is:
A. B < Al < Ga < In < Tl B. B < Ga < Al < In < Tl C. Tl < In < Ga < Al < B D. B < Al < In < Ga < Tl
4. The anomalous behaviour of boron among Group 13 elements is mainly due to:
A. Large size and low ionisation enthalpy B. Small size, high ionisation enthalpy and absence of d-orbitals C. Presence of vacant d-orbitals D. Metallic nature
5. Which Group 13 element is a metalloid?
A. B B. Al C. In D. Tl
6. Boron does not form B3+ ion readily because:
A. Boron has low ionisation enthalpy B. Boron has a very large atomic size C. Removal of three electrons requires very high energy D. Boron has three lone pairs
7. Which of the following compounds is electron deficient?
A. NH3 B. CH4 C. BF3 D. H2O
8. The hybridisation of boron in BF3 is:
A. sp B. sp2 C. sp3 D. dsp2
9. BF3 acts as a Lewis acid because:
A. It contains a lone pair on boron B. Boron has an incomplete octet C. Fluorine donates electrons permanently D. It contains a positive charge
10. Which of the following is the strongest Lewis acid?
A. BF3 B. BCl3 C. BBr3 D. BI3
11. The Lewis acidity order of boron trihalides is:
A. BF3>BCl3>BBr3>BI3 B. BF3<BCl3<BBr3<BI3 C. BI3<BBr3<BCl3<BF3 D. BCl3<BF3<BI3<BBr3
12. The comparatively low Lewis acidity of BF3 is due to:
A. Hydrogen bonding B. Strong pπ−pπ back bonding C. Ionic character D. Steric hindrance
13. Borax has the formula:
A. Na2B4O7 B. Na2B4O7⋅10H2O C. NaBO2 D. NaBH4
14. Orthoboric acid is:
A. Monobasic B. Dibasic C. Tribasic D. Tetrabasic
15. Boric acid behaves as a Lewis acid because:
A. It donates H+ directly B. It accepts OH− from water C. It releases H− D. It contains a B–B bond
16. The correct formula of orthoboric acid is:
A. HBO2 B. H2B4O7 C. H3BO3 D. HBO3
17. When boric acid is heated strongly, the final product formed is:
A. B2O3 B. BO2 C. B2H6 D. B4C
18. Which of the following is used in the preparation of boric acid?
A. Borax + HCl B. B2O3+NaOH C. BF3+H2 D. AlCl3+H2O
19. Diborane (B2H6) contains:
A. Only normal 2-centre–2-electron bonds B. Only 3-centre–2-electron bonds C. Four B–H terminal bonds and two bridging B–H–B bonds D. Six bridging hydrogen atoms
20. The number of 3-centre–2-electron bonds in diborane is:
A. 1 B. 2 C. 3 D. 4
21. Which of the following is used as a reducing agent?
A. BF3 B. B2H6 C. B2O3 D. H3BO3
22. Aluminium chloride exists as a dimer Al2Cl6 in the vapour phase at lower temperature. The dimer contains:
A. 2 coordinate bonds B. 4 coordinate bonds C. 6 coordinate bonds D. No coordinate bonds
23. Aluminium chloride is electron deficient because aluminium in AlCl3 has:
A. 2 electrons around it B. 4 electrons around it C. 6 electrons around it D. 8 electrons around it
24. Which of the following oxides is amphoteric?
A. B2O3 B. Al2O3 C. Tl2O3 D. B2O3 and Al2O3
25. The acidic character of Group 13 oxides generally:
A. Increases down the group B. Decreases down the group C. Remains constant D. First decreases then becomes zero
26. Which of the following compounds is formed when aluminium reacts with NaOH and water?
A. AlCl3 B. Na[Al(OH)4] C. Al2O3 D. NaAlO2 only, under all conditions
27. The correct order of stability of oxidation states for thallium is:
A. Tl3+>Tl+ B. Tl+>Tl3+ C. Tl2+>Tl+ D. Tl5+>Tl3+
28. The inert pair effect in Group 13 is maximum for:
A. B B. Al C. In D. Tl
29. Which of the following statements about boron is incorrect?
A. It is a metalloid. B. It does not form B3+ ion easily. C. It forms electron-deficient compounds. D. It readily forms B3+ in aqueous solution.
30. Which one of the following pairs is incorrectly matched?
A. B2O3 — Acidic oxide B. Al2O3 — Amphoteric oxide C. Tl2O3 — Basic oxide D. BF3 — Lewis base
Cannabinoids interact mainly with cannabinoid receptors in the brain.
Natural cannabinoids are obtained from the inflorescences of Cannabis sativa.
Cannabis products include:
Marijuana
Hashish
Charas
Ganja
They can affect the cardiovascular system.
4. Cocaine
Cocaine is a coca alkaloid.
Obtained from Erythroxylum coca.
It interferes with the transport of the neurotransmitter dopamine.
Common names: coke, crack
It has a powerful stimulant effect on the CNS.
It can produce euphoria and increased energy.
Excessive doses can cause hallucinations.
5. Hallucinogenic plants
Important examples:
Atropa belladonna
Datura
These plants have been used historically in folk medicine and religious rituals.
6. Other drugs that may be abused
Examples include:
Barbiturates
Amphetamines
Benzodiazepines
Although many have legitimate medical uses, their misuse can be harmful.
Tobacco and Smoking
Nicotine
Tobacco contains nicotine, an alkaloid.
Nicotine stimulates the adrenal gland.
This causes release of:
Adrenaline
Nor-adrenaline
Effects:
Increased blood pressure
Increased heart rate
Harmful effects of smoking
Smoking is associated with increased risk of:
Lung cancer
Urinary bladder cancer
Throat cancer
Bronchitis
Emphysema
Coronary heart disease
Gastric ulcer
Tobacco chewing
Associated with increased risk of oral cavity cancer.
Carbon monoxide
Smoking increases CO concentration in blood.
CO binds strongly with haemoglobin, forming carboxyhaemoglobin, thereby reducing the oxygen-carrying capacity of blood and causing oxygen deficiency in tissues.
Sarvan sir- Chemistry For All 