Biology Chapter 1 Reproduction In Organisms

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(i) Juvenile phase. The period of growth in life of organisms before they start reproducing sexually and attain a level of maturity is called juvenile phase. It is known as Vegetative phase in plants.

(ii) Reproductive phase. The period of active reproductive behaviour when the organisms show marked morphological and physiological changes is called reproductive behaviour. It is followed by senescence phase.

 Budding in Saccharomyces.

 Leaf of Bryophyllum with young plants.

Disadvantages of external fertilization are :

(1) A large number of gametes are produced to ensure fertilization thus there is wastage.

(2) The offsprings formed are extremely vulnerable to predators and are risk upto adulthood.

(3) The gametes and zygotes face a greater risk of dessication.

1. The fusion of gametes and genetic recombination,  causes variations in the offsprings thus, also forms the raw material for evolution.

2. The offsprings adapt more comfortably and quickly to the changes in environmental conditions and the survival rate is high.

3. Any mutation or disease present in the parents may not appear in the progeny due to variation in genes.

4. Sexual reproduction plays an important role in the origin of new species.

Scientific Names of flowers

Common Name Scientific Name

1. Rose -  Rosa indica

2. Sun flower - Helianthus annus

3. Petunia - Petunia alba

4.  Hibiscus - Rosa sinensis

5. Pea - Pisum sativum.

Viviparous animals. The animals which give birth to young ones and fertilization and development are internal nutrition is obtained from mother. Examples. Rat, Rabbit, Human.

Monkey — 26 years ;          Dog — 13-15 years ; 

Cat — 12-15 years ;            Horse —25-30 years :

Elephant — 65 years ;         Eagle — 20 years ;

Man — 85 years :                Parrot — 80-100 years;

Tortoise — 150 years ;   Banyan tree — 200 years ;

Sequoia tree — 3000 - 4000 years.

Oldest living tree is the Bristle Cone Pine in the White Mountains (California), with an age of 5,065 years.

(ii) Vegetative reproduction is also considered as a type of asexual reproduction because it does not involve  fusion of male and female gametes and require only one parent. New plants are produced by vegetative parts of plants without the formation of seeds or spores . 

(a) Fission (Binary and Multiple fissions)
(b) Budding
(c) Fragmentation
(d) Gemmulation
(e) Vegetative propagation and
(f) Sporulation.

1. It involves a single parent and their is no need to search for mate.

2. Reproduction is rapid and may produce large number of young ones.

3. It requires less time and energy.

Disadvantages of asexual reproduction

1. Their is no genetic variation.

2. If the parent has and disease the offspring also has it, because it is identical to its parent.

3. The offspring is not fit to adapt to the changing environment and chances of survival are less.

Examples.
1. In Century plant (Agave sp.) flowers, buds develop into bulbils which drop to the ground and develop into new plants.
2. Potato tubers possess buds which grow into new plants.

1.Fusion of two gametes, genetic recombination, interaction etc. take place which causes variations in the offsprings ,thus it  also forms raw material for evolution.

2. The offsprings adapt more comfortably and quickly to the change in environmental conditions and have better chances of survival.

Disadvantages of sexual reproduction.

1.Usually two parents of opposite sexes are required (except in hermaphrodite).

2. It consumes more time and energy.

Different kinds of asexual structures are represented below:

Fig. Different kinds of asexual structures.
A. Zoosporangium producing motile zoospores
B. Conidiophore of Penicillium bearing conidia;
C. Buds in Hydra D. Gemmules in sponges
D. Gemmules in sponges.

(i) Binary fission. It is the simplest method of asexual reproduction generally found in unicellular organisms like Amoeba, Paramecium, Euglena etc. Binary means two and fission means breaking, thus this process involves the division of animal body into two parts.

After attaining an optimum size the adult undergoes division. It is completed in two steps. First the nuclear division followed by cleavage of cytoplasm into two parts each having a daughter nucleus. Amoeba and Paramecium divide in transverse plane and Euglena in longitudinal plane.

 Binary Fission in Amoeba

(ii) Multiple fission. It is a type of asexual reproduction in which nucleus undergoes repeated divisions before the cytoplasm breaks to form a number of uninucleate daughter cells. Each body thus formed grows into a new individual. Multiple fission occurs in Amoeba and Plasmodium during the formation of merozoites (schizogony), sporozoites (sporogony) and male gametes (Gamogony). It is also quite common in Amoeba and other acellular organisms.

 Spore formation in Amoeba.

Budding. It is a common method of reproduction in Sponges and Hydra. In this process, the new individual develops from a small outgrowth on the surface of parent. The exogenous bud gets its nourishment from the parent till it gets the maturity. Then it breaks off from the parent body and develops into new individuals. Sometimes, the buds do not separate off and form parent.

Fig. Budding in Hydra.

   Gemmule of Spongilla.

(1) Gametogenesis( by meiosis) -Development of male and female gametes which are haploid in nature .

(2) Fertilization- Fusion of the two gametes (haploid cells) to form zygote (diploid cell).

(3) Embryogenesis- Mitotic divisions and cell differentiation of zygote to form embryo. mitosis helps in increasing the cell number and differentiation helps to form specialized tissues and organs.

(4) Development - Growth  of embryo to form new individual.

(a) Ovary → diploid (2n)

(b) Anther → diploid (2n)

(c) Egg → haploid (n)

(d) Pollen → haploid (n)

(e) Male gamete → haploid (n)

(f) Zygote → diploid (2n)

1. The fusion of male and female pronuclei in fertilization restores the diploid number of chromosomes.

2. Fertilization initiates cleavage or segmentation.

3. The combination of the chromatin material from two different parents form the physical basis of biparental inheritance and variation.

It is of two types :

A. Natural Vegetative propagation

1. Vegetative propagation by stem. e.g. grasses, turmeric, onion, colocasia, potato, gladiolus and crocus.

2. Vegetative propagation by roots. e.g., Tuberous roots of sweet potato, asparagus, tapioca, dahlia and yams (Dioscorea).

3. Vegetative propagation by leaves e.g. Bryophyllum, Begonia, Lilium.

4. Vegetative propagation from reproductive organs. Flower buds of century plant (Agave sp.) develop into bulbils.

B. Artificial vegetative propagation.

1. Cutting e.g. leaf cutting in Bryophyllum.

2. Layering e.g. Jasmine.

3. Grafting e.g. Rose, Mango.

4. Micro-propagation.

5. Gootee e.g. lemon, orange, guava, litchi

(1) Plants produced by vegetative propagation are genetically similar and constitute a uniform population called as clone.

(2) Plants that have reduced power of sexual reproduction, long dormant period of seed, poor viability can be  multiplied by vegetative methods.

(3) Some fruit trees like banana, pineapple  that do not produce viable seeds and dub grass which produces small quantity of seeds can  be  propagated by vegetative methods.

(4) It is a rapid and easier method of propagation.

(5) Good characters can be  preserved by vegetative propagation.

(6) Vegetative Propagation can be used to develop Virus Free plants.

(7) Grafting helps in getting an economically important plant having useful characteristic of  two different individuals in short time in a single plant.

Gametogenesis is the process of gamete production while meiosis is the process of reduction division in which the chromosome number is reduced to half. In order to produce gamete which are haploid in nature the cells have to undergo meiosis. The chromosome number is reduced to half in the two successive meiotic cycles. Thus, meiosis and gametogenesis are always interlinked. 

After fertilization the zygote is formed. The zygote then undergoes many division by the process of mitosis, to form an embryo by a process called embryogenesis. The ovule of the flower develops into a seed which along with the embryo is covered by a protective seed coat.  The sepals, petals and stamens of the flower wither and fall off. The ovary forms the fruit which is covered by a protective thick wall called pericarp. The seeds germinate on meeting favourable conditions. 

Cucurbits are unisexual plants. The staminate or male flowers are bright, yellow coloured. The staminate flowers bear bright, yellow coloured petals bearing stamens. Whereas, the pistillate flowers have pistil. Other examples of unisexual flowers are papaya, cucumber, etc.

Oviparous animals lay eggs outside of their body. Thus, the eggs have to face the harsh environmental conditions like excessive heat or cold, predators, water scarcity etc. On the other hand, in viviparous animals, the development of the egg takes place inside the body of the female. The egg is well protected from the unfavourable conditions. Hence, the offspring of an egg-laying or oviparous animal is at greater risk as compared to the offspring of a viviparous animal, which gives birth to its young ones.

Zooplankton under unfavorable enters ‘diapause’ which is a state of suspended development.

Organisms such as fungi and algae switch to sexual mode of reproduction during adverse conditions because sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed conditions and survive. This ensures the continuity of species.

Double fertilization occurs in plants of both castor and groundnut but the mature seeds of groundnut are non-albuminous and castor are albuminous. The post fertilization events that are responsible for it are:

The primary endosperm nucleus divides repeatedly to give rise to a free nuclei and the stage of endosperm development is called free nuclear endosperm. The cell wall forms after giving rise to a cellular endosperm.

If the endosperm is fully consumed by the growing embryo then non-albuminous seeds are formed as in groundnut. If the endosperm is retained then it forms albuminous seeds as is the case with castor plant.

The number of viable seeds produced by the tomato plant through sexual reproduction = 240

(a) The minimum number of pollen grains that must have been involved in the pollination of its pistil are 240 because each pollen grain contains two male gametes. Out of these two gametes, one fuses with polar nuclei and forms endosperm, while, the other male gamete fuses with the egg cell to form the zygote that eventually give rise to seeds. Therefore, in order to obtain 240 seeds, number of pollen grains needed would be 240.

(b) The minimum number of ovules involved in this process would be 240, as the number of viable seeds is 240. After fertilisation, the ovary turns into fruit and the ovules turn into seeds. Therefore, the number of ovules corresponds to the number of seeds formed.
(c) During the process of gametogenesis, 240 megaspore mother cells are involved as only one megaspore of the tetrad becomes functional and develops further and the rest three megaspores get degenerated.

(d) In the above case, 60 microspore mother cells must have undergone reduction division prior to dehiscence of anther, as each microspore mother cell would give rise to 4 microspores. Since 1 microspore mother cell would produce 4 microspores, therefore, to obtain 240 microspores, there must be 60 microspore mother cells.

(e) The number of male gametes involved in seed formation would be 240 as each male gamete will fuse with one egg nuclei to form zygote, which will further give rise to the seed.

Tapetum nourishes the developing pollen grain so in case of a  malfunctioning tapetum the pollen grain will not get any nourishment and lose its viability.

In geitonogamy the pollen grains are transferred from the anther to the stigma of another flower on the same plant, thus functionally it involves cross-pollination. Since the pollen grains come from the plant it is genetically similar to autogamy.

(a) The gamete contains haploid set of chromosomes while the meiocyte contains a diploid set.

(b) Whiptail lizard is parthenogenetic because in this animal, an unfertilized egg develops into a new individual. This process of reproduction without fertilization is called parthenogenesis.

The type of cell division occurring in the zygote of an organism exhibiting haplontic life cycle is meiosis.

Mosses are bryophytes and they need water for fertilisation. During the transfer of male gametes, many of them are destroyed or lost. Thus, moss plants produce very large number of male gametes to compensate for the loss during transport.
These male gametes are called antherozoids.

Meiocytes are specialised cells present in sexually reproductive organisms. They undergo meiotic division to produce male and female gametes that carry only one set of chromosomes and thus help in maintaining the chromosomal number of the organism. 

The phase that all organisms have to pass through before they can reproduce sexually is Juvenile phase. It is known as Vegetative phase in plants.

Streptokinase enzyme is produced by the bacterium Streptococcus.
It is used as a ‘clot buster’ which removes clots from the blood vessels of patients who have undergone myocardial infarction.

A. The thermal plants release particulate matter, which is considered very harmful for the human health. The electrostatic precipitator helps in the removal of particulate matter and can remove over 99 per cent of it present in the exhaust of the thermal power plant.
It has electrode wires that are maintained at several thousand volts. These produce a corona that releases electrons. The electron attach to the dust particles giving them a negative charge. The collecting plates of the precipitator are grounded and thus attract the charged dust particles. The scrubber removes gases like sulphur dioxide. 
Four important methods that can be implemented to reduce pollution
1. Use of lead-free petrol .
2. Catalytic converter such as platinum-palladium and rhodium should be used for decreasing emission of poisonous gases.
3. Use of CNG.
4 . Reducing the sulphur and aromatic content in petrol and diesel fuels. 

Parthenogenesis

In most plants, flowers need to be pollinated and fertilized to produce fruits. However, some plants can produce fruits before fertilization or without fertilization. Parthenocarpy is the process which produces fruits from unfertilized ovules in plants. Unfertilized ovules develop into fruits prior to fertilization. These fruits do not contain seeds.

Parthenogenesis is a type of reproduction commonly shown in organisms mainly by some invertebrates and lower plants. It can be described as a process in which unfertilized ovum develops into an individual (virgin birth) without fertilization. Therefore, it can be considered as a method of asexual reproduction.

It is seen in organisms like rotifers, honeybees and even some lizards and birds (turkey). The key difference between parthenogenesis and parthenocarpy is, parthenogenesis is shown by animals and plants while pathenocarpy is shown only by plants.

A.

If both assertion and reason are true and reason is the correct explanation of assertion.

Females having 45 chromosomes (2A + XO) are affected with Turner's syndrome. Individuals having Turner's syndrome have female sexual differentiation but ovaries are rudimentary. Other associated phenotypes of this condition are short stature, webbed-neck, broad chest, lack of secondary sexual characteristics and sterility. Thus, any imbalance in the copies of the sex chromosomes may disrupt the genetic information necessary for normal sexual development.

D.

1,2 and 4

Common cold can take place from one person to other as it is a communicable in nature. A healthy person can get infected by being in close vicinity of infected person when he/she sneezes, coughs, as the droplets generated by sneeze and cough contain infecting agents. Typhoid occurs by the intake of contaminated water & food. While ringworm is one of the skin disease which can transfer from one person to other by the use of infected towel & handkerchief. AIDS (Acquired lmmuno deficiency) does not occur or transfer by shaking hands.

B.

Histones are acidic in nature that forms core for DNA packaging.

According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health. These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, such as irritation, inflammations and damage to the lungs and premature deaths.

B.

Cryptic camouflage is seen in Biston betularia

The peppered moth (Biston betularia) is a temperate species of night-flying moth. Peppered moth evolution is often used by educators as an example of natural selection. Peppered moths are cryptically camouflaged against their backgrounds when they rest on the tree trunk.

D.

upper oogonium and lower antheridium on the same plant

Monoecious or homothallic, a condition in Chara (green algae) is used to denote upper oogonium and lower antheridium on the same plant. The organisms, which possess both the reproductive organs are bisexual. Unisexual condition represents both male or female organs in the same organism.

C.

The plant body Sargassum is a diploid sporophyte.  It does not multiply asexually by means of spores. Instead it reproduce by vegetative means, i.e. fragmentation which is the only known method of vegetative reproduction in the free floating species of Sargassum. 

A.

PCR and RAPD

RAPD stand for Random Amplified Polymorphic DNA. It is a type of PCR reaction, but the segments of DNA that are amplified are random. Often, PCR is used to amplify a known DNA sequence. 

C.

Ectocarpus

Male gametes are flagellated in Ectocarpus belonging to Phaeophyceae. The flagella of male and gamete plays an important role in establishing initial sexual contact with the female gamete. However, in Ectocarpus the female gamete too is flagellated but is different in structure. 
In Polysiphonia (Rhodophyceae) flagellated gametes are not observed, in Anabaena sexual reproduction through gametes is absent while in Spirogya sexual reproduction takes place by conjugation wherein male gamete passes through a tube to the adjacent filament. The male gametes here are non-flagellated and show amoeboid movement. 

D.

Recombination

Recombination is the most common mechanism of genetic variation in the population of a sexually reproducing organism. It involves the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome. This mechanism is generally mediated by homologous chromosomes, during meiosis, i.e, formation of gametes or germ cells. 

B.

(i) Phytophthora belongs to Phycomycetes (algal fungi). They contain either unicellular thallus or non-separate coenocytic mycelium. They are mostly plant damaging Oomycetes (water molds).
(ii) Alternaria is Deuteromycetes (fungi imperfecti), which lacks sexual reproduction.
(iii) Mucor also belong to Phycomycetes. They have mycelium which is coenocytic (multinucleate) and profusely branched. They reproduce vegetatively via conjugation.
(iv) Agaricus belongs to Basidiomycetes (where karyogamy and meiosis occur). They contain well-developed filaments, branched and septate mycelium. They are saprophytic but parasitic.
So, hence (b) option is correctly matched.

C.

Male shark - claspers borne on pelvic fins

A clasper is a male anatomical structure found in some groups of animals, and used in mating. Male cartilaginous fish like shark hacve claspers formed from the posterior portion of their pelvic fin which serves as intromittent organs used to channel semane into the female's cloaca during mating.

D.

Marchantia

In Marchantia, a bryophyte, the archegonia (female sex organs) are borne on special branches called archegoniophore or female receptacles. Each archegoniophore has rows of archegonia protected by involucre or perichaetium.

D.

Both produces progeny identical to the parent

Both vegetative and apomixis are an asexual reproduction. The progeny produced are genetically similar to a parent and are called clone.

A.

Marchantia, a liverwort, is dioecious. The female thallus bears female sex organs called archegonia on special branches called archegoniophores. The plant's body is anchored by unicellular rhizoids.

D.

Bean

The bean or legume family is one of the most common plant families. Flowers in bean family typically have their two bottom petals grown together along one side forming a structure a bit like a narrow but deep scoop. This special Bean- family kind of two -in-one petal is called the keel, like the keel of a boat. Bean blossoms with the configuration are said to be papilionaceous.

B.

Pinus

Pinus is monoecious, which bear male cone as well as a female cone on the same tree on separate branches.
Marchantia Cyas and papaya are dioecious plants

B.

in the eight cell stage, cells are separated and cultured until small embryos are formed which are implanted into the womb of other cow

In cloning of cattle a fertilized egg divides in 2, then in 4 and then in 8. This embryo is carefully removed from the womb. The embryonic cells are then separated using enzyme. Each isolated cell is kept in a nutrient medium and later implanted in the womb of a different 'host mother' cow.

D.

Two

The types of gametes produced by a plant depend upon the number of hetrozygous pair.
Number of types of gametes  = Zⁿ
   n = number of heterozygous pair
                 2¹ = 2
The gametes are  - ABC and AbC.

A.

Saccharomyces

1. Saccharomyces i.e. yeast is a eukaryote (unicellular fungi)
2. Mycobacterium – a bacterium
3. Oscillatoria and Nostoc are cyanobacteria

C.

Sexual reproduction

Parthenogenesis is a form of sexual reproduction n which the ovum develops into a new individual without fertilisation.

C.

In Trygon, the male introduces sperms into female through a modified pelvic fin.

Mating in dogs is not synchronised with lunar cycle. Six of the nine families of Salamanders have internal fertilisation. Catla has external fertilisation.

B.

Ti plasmid

The DNA used as a carrier for transferring a fragment of foreign DNA into a suitable host is called vehicle DNA or cloning vector. The Ti plasmid is present in Agrobacterium tumefaciens. It is a Gram negative soil bacterium that infects a wide range of plants and causes tumorous growth especially at the root or stem junction (crown gall). 

Ti plasmid can be used as a DNA vector by replacing the tumour inducing genes with the gene of interest and a marker gene to enable selection of transformed cells.

D.

(ii) > (i) > (iii)

Seminal vesicles produce an alkaline secretion which forms 60% of the volume of semen. Its secretion include fructose, prostaglandins, citrate, inositol and clotting proteins.

Prostate gland produces a milky and slightly alkaline secretion whch forms 25% of the volume of semen. It consists of Calcium, Phosphate, Bicarbonate, enzyme prefibrolysin, clotting enzymes and prostaglandins. 

Bulbourethral glands or Cowper's glands also secrete an alkaline fluid which neutralizes acids from urine in the urethra. Its secretion is the least but is of great importance.

A.

Progestasert

Progestasert is a hormone releasing IUCD which makes the uterus unsuitable for implantation and cervix hostile to the sperms.

Lippe's loop is non- medicated IUCD.

CuT and Multiload are copper releasing IUCDs, which suppress motility and fertilizing capacity of sperms.

A.

800$°$C

Initially, Oparin and Haldane proposed that first form of life could have come from pre- existing non- living organic molecules. The conditions were high temperature, volcanic eruption , storms, reducing atmosphere consisting of CH₄, NH₃ etc. Later in 1953, Miller created similar conditions in a laboratory and created an electric discharge in a closed flask containing CH₄, H₂ and NH₃ and water vapour at 800$°$C.

B.

Human RBC

Inside human RBCs, merozoites stop moving with erythrocytic cycle to increase in size and become rounded gametocytes. Male gametophytes or microgametocytes are smaller and contain a large diffused nucleus. Female gametophytes or mega gametophytes are larger with a small compact peripheral nucleus. They do not divide but give rise to gametes in insects.

D.

cannot be degraded

Exine is the outer layer of pollen grain. It is thick and smooth and culticularised. Sporopollenin is the cutin. It protects the pollen grains as microfossils. It is not degraded by enzyme. It is not affected by high temperature, strong acid or alkali. It is resistant to chemical and biological decomposition.

A.

30

Pollen viability is the period for which pollen grains retain the ability to germinate. It is little in flowers which are pollinated in bud condition. Eg, it is 30 minutes in rice and wheat. It depends upon environmental conditions of temperature and humidity.

B.

1 diploid and 1 triploid cell

Double fertilization is the fusion of two male gametes with a female gametophyte. It is found only in Angiosperms.

In angiosperms, the pollen tube bursts open in one of the two synergids to release the two male gametes. One male gamete fuses with the egg to form a diploid zygote and is known as generative fertilization. The second male gamete descends down and fuses with the diploid secondary nucleus of the central cell to form a triploid primary endosperm cell and is known as vegetative fertilization.

After double fertilization, mature angiospermous ovule contains one diploid cell (zygote) and one triploid cell (endosperm).

A.

recombinant DNA technology

Genetically modified (GM) crops or transgenic plants are the plants in which a foreign gene has been introduced and integrated into the host DNA via RDT (Recombinant DNA Technology). It results in the production of desirable traits like disease resistance, insect resistance, herbicide resistance etc.

C.

5' - GAATTC - 3'

3' - CTTAAG - 5'

A palindromic sequence is a sequence made up of nucleic acids within double helix of DNA and/ or RNA that is same when read from 5' to 3' on one strand and 5' to 3' on the other. Eg, 

D.

In family A, both the parents are heterozygous recessive.

In family A, if both the parents are homozygous recessive, then both should be diseased and should have 100% diseased progeny.

In family B, if both the parents are homozygous dominant, they would not have got the recessive disease in first place.

In family B, if both are heterozygous recessive, then also, they would not have got the disease, neither 80% of progeny would be diseased.

D.

cells of trophoblast, in contact with inner cell mass of blastocyst.

The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. Inner cell mass looks like a small knob at one pole which gives rise to the embryo and is called the embryonal knob. The trophoblast does not take part in the formation of the embryo proper. It remains external to the embryo and gives rise to the extraembryonic membranes, namely, chorion and amnion, for the protection and nourishment of the embryo. The trophoblast cells in contact with the embryonal knob are known as cells of Rauber.

D.

A: Carrying capacity

The given figure shows population growth curve, in which A is carrying capacity, B is exponential growth curve and C is logistic growth curve

C.

Signal for parturition comes from fully developed foetus and placenta.

Parturition is induced from the fully developed foetus and the placenta. Parturition involves foetal ejection reflex which are mild contractions of the placenta. This reflex triggers release of oxytocin from the maternal pituitary which acts on the uterine muscles and causes stronger uterine contractions and that further stimulates secretion of oxytocin. This stimulatory reflex between uterine muscle contraction and oxytocin secretion continues resulting in stronger contractions and eventually leading into expulsion of the baby out of the uterus.

C.

Rice

India produces the largest variety of rice.

B.

methanogenic bacteria in rumen

Cattle ranching refers to practice of raising grazing livestock such as cattle or sheep for meat and wool, etc. The area of landscape meant primarily for cattle ranching is called a ranch. The practice has lead to accelerated deforestation and contributed to increased methane gas concentration in atmosphere. Whatever cattle eat; is subjected to the action of methanogens (bacteria) harbouring the stomach (rumen) of cattle. The action of these bacteria on food material produces methane gas which is released through cattle fart into the earth's atmosphere where it absorbs heat just like carbon dioxide, contributing to global warming.