BIOLOGY INVESTIGATORY PROJECTAdaptations in plants and animals

of xerophytic condition

SUBMITTED BY:

CLASS: XII

CERTIFICATE

This is to certify that this “Biology Investigatory project” on the topic ADAPTATION OF PLANTS AND ANIMALS IN XEROPHYTIC CONDITION has been successfully completed by -----------------of class XII under the guidance of ---------------------in particular fulfillment of the CENTRAL BOARD OF SECONDARY EDUCATION leading to the award

of annual examination of the year---------------

TEACHER IN CHARGE: EXTERNAL EXAMINER:

PRINCIPAL:

ACKNOWLEDGEMENT

This project would not have been possible with the help of my Parents, my biology teacher ------------------------and my Friends.

I sincerely thank our biology teacher ----------------for her continuous support.

Arunima.R

INDEX

S.No CONTENTS PAGE No 1. Certificate 3

2. Acknowledgement 4

3. Introduction 6

4. Xerophytic Adaptation 7

5. Xerophytic plants and their adaptation

8

6. Species and special adaptation

17

7. Xerophytic animals and adaptation

22

8. Some special features of xerophytic animals

31

9. Species and special adaptation

33

10. Summary 41

INTRODUCTION

Plant and animal bodies are made up of a number of complex biological processes which take place within a narrow range of temperatures. If the temperature increases or drops below this range, the organism dies. The problem with a desert ecosystem is that temperatures reach or sometimes exceed the limits that are conducive for carrying out life sustaining processes.Add to it, the scarcity of water, which translates to the scarcity of the very basic requirement for every living organism. To survive in such harsh environment, animals have developed certain features that have enabled them to not only survive but thrive in the desert. Plants and animals living in the desert must be able to adapt to extreme heat and dryness, and the desert’s harsh environment. The deserts are very hot during the day but will cool during the evening. There is constant sunlight almost daily. Plants and animals also need to be able to adapt to strong winds, limited access to water and extreme temperatures.

XEROPHYTIC ADAPTATION

What are xerophytes?

There have been many interpretations of the term xerophytes, sometimes they are loosely defined as plants and animals of dry habitats.

Xerophytic plants and their adaptation

In arid zones, all plants not confined to the margins of streams or lakes have been considered as xerophytes, whereas in regions of heavy rainfall the class would be represented only by shallow-rooted plants of sandy soils, by ' plants of dry ridge tops, and by algae, mosses and lichens which grow on trees barks or rock surfaces etc.The true nature or xerophytes is not clearly understood. For example, it is difficult to decide whether a xerophyte is really xerophilous and occurs only in dry habitats and deserts or it is merely drought-resistant.

ALEO EUPHORBIA OPUNTIA

1. Morphological features

a. RootsIn contrast with hydrophytes which develop in conditions with plenty of water, Xerophytes develop under water deficient conditions. The main purpose of roots is to secure water, which is present in fewer amounts and in deep layers of soil. The root system is the most important organ for the survival of plant and thus is very well developed. The roots have following characteristics.

1. It is very well developed and in some cases is several times longer than shoot. Roots are long, tap roots with extensive branching spread over wide areas.

I

2. Root hair and root caps are very well developed.

b. Stems1. Mostly the growth of stem is stunted, woody, dry, hard, ridged

and covered with thick bark

2. in some as Saccharurn stem becomes underground, whereas in opuntia if becomes fleshy, green, leaf-life (phylloclade) covered with spines. In Euphorbia also it becomes fleshy and green.

3. on stems and leaves, there are generally hairs and/or waxy coatings.

c. Leaves

1. Leaves are very much reduced, small, scale-like appearing only for a brief period sometimes modified into spines. Lamina may be long, narrow or needle-like as Pinus or divided into many leaflets as in Acaia .

2. Foliage leaves when present may become thick, fleshy and succulent or, tough and leathery in texture.

3. Leaf surface is mostly shiny and glazed to reflect light and heat.

4. In some species leaves become folded and rolled in such a manner that the sunken stomata become hidden and thus rate of transpiration is minimized.

2.Anatomical features

a. Roots 1. Root hairs and root caps are well developed. In Opuntia root

hairs develop even at the root tips.

2. In Asparagus roots may become fleshy to store water.

b. Stems

1. in succulent fleshy xerophytes, such as Casuarina, following chief characteristics is present (Fig).

a) Cuticle is very thick, b) Epidermis is well developed, with heavily thickened cell walls, c) Hypodermis is several-layered and sclerenchyrnatous. d) Stomata are of sunken type e) Vascular tissues are very well developed, differentiated, and

heavily lignified. Vascular bundles have well developed several layered bundle sheath.

f) Mechanical tissues are very well developed i) Bark is very well developed ii) Oil and resin are often present

T.S OF A STEM

c. Leaves1. In succulent leaves of malacophyllous xerophytes, such as

Peperomia, epidermal cells of leaves serve as water-storage organs. Similarly, succulent leaves of Aloe have prominent water-storage regions in their mesophyll. The cuticle is thick and outer walls of epidermal cells are heavily deposited with cutin and cellulose.

2. Non succulent xerophytes, such as Nerium and Pinus have following characteristic features:

a) The cuticle is heavy and well developed.b) Epidermis is several layered in Nerium and in Pinus hypodermis is

several layer.c) Mesophyll is very well differentiated into palisade and spongy

parenchyma.d) Stomata are of sunken type confined to lower epidermis, in some

xerophyte, for example in Nerium stomata are situated in pits lined with hairs.

e) Vascular tissues are very well developed, differentiated into xylem with lignified elements and phloem.

f) Mechanical tissue is very well developed, including several kinds of sclereids.

T.S OF LEAF

FEATURES OF A XEROPHYTIC PLANT

XEROPHYTIC FLORA

Palo Verde Tree

The leaves are very small (and fall off quickly in dry times). Leaves lose water far more easily than bark, so this helps the tree survive in arid environments.

Prickly Pear

They have no leaves, their roots are shallow, their stems are shaped like pads and store water, and they have spines for shade and waxy skin to seal in moisture.

SPICIES AND SPEACIAL ADAPTATIONS

Saguaro

Aside from their taproot that extends 2 feet or more into the ground, the rest of their roots are rarely more than 4 inches deep. They radiate horizontally about as far as they are tall.

Agave

They have a rosette (rounded) shape. This shape helps capture rainwater and channel it to their base.

Ocotillo

They are drought–deciduous which means they can produce full grown leaves within 3 days of summer rain, but they turn yellow and fall off after a couple of weeks of dry weather.

Jojoba

The vertical orientation of their leaves is an adaptation to the extreme desert heat. This means the largest surface of their leaf is facing the sun most directly in morning and late afternoon and the smallest surface is facing the sun in the hottest parts of the day.

Brittlebush

They have fuzzy, light colored leaves that reflect sunlight. This helps reduce their leaf temperature and helps them conserve water.

Creosote

They can live for at least 2 years with no rain, losing their leaves and even shedding branches to reserve the last bits of water and nutrients for the crown. Sometimes people say they smell like rain.

Palo Verde Tree

Their leaves are very small (and fall off quickly in dry times). Leaves lose water far more easily than bark, so this helps them survive in arid environments. The bark is green.

Mesquite Tree

They have adapted to desert conditions by developing an extremely long root system to draw water from deep underground near the water table. Their roots are considered the longest of any desert plant and have been recorded as long as 160 feet.

Xerophytic animals and their adaptations

Animals of the desert need to adapt to intense heat and lack of water and shelters. Many of the desert animals are only active during the evening when the temperatures are cooler. Other animals burrow during the day to avoid the harsh conditions during the day. It is difficult for large animals to survive the desert due to the lack of shelter to hide from prey. Some animals don’t need to drink water as they get all the water they need from the insects, plants and seeds that they eat. Many desert animals don’t have sweat glands which lets them retain moisture eliminating the need to drink. Birds have feathers that keep them insulated from the strong heat of the sun. Some rodents have specialized kidneys that return their water to the bloodstream instead of losing it through urination. Desert animals include many reptiles, insects, birds and small mammals. Camels, Frogs, Lizards, Bobcats, Golden Eagles, Kangaroo Rats, Spade foot Toads.

Adaptive features of Desert animals

To Avoid Heat

Most animals avoid being out in the sun during the hottest part of the day.

Many mammals, reptiles, and amphibians live in burrows to escape the intense desert heat. Rodents also plug the entrance of their burrows to keep the hot and dry winds out. Most animals either come out during the early morning or in the evening.

Some animals like snakes, foxes, and most rodents are nocturnal. They sleep during the daytime in their burrows or dens and hunt only during the night when the temperatures drop.

Certain animals like the round-tailed ground squirrel resort to aestivation (a long state of inactivity) when they slow down their metabolism to conserve water and energy when the days become very hot.

To Dissipate Heat

Due to constant exposure to high temperatures, these animals need to regulate their body temperatures, to carry out the various processes that are important for their survival.

Some have developed long body parts that provide greater body surface to dissipate heat. For example, jackrabbits have large ears that are supplied with a large number of blood vessels that enables excess heat to be dissipated easily. It is a known fact that light colors are poor absorbers of heat.

Most desert animals are pale in color which prevents their bodies from absorbing more heat in the sun.

Turkeys and black vultures are dark in color and hence they absorb considerable amount of heat during the day.

To prevent their bodies from overheating, they undergo the process of urohydrosis. They urinate on their legs that have numerous blood vessels. The heat gets absorbed as the urine evaporates, thereby cooling their bodies.

To Absorb Water

Insects and reptiles of the desert have impervious integument and excrete nitrogen in the form of uric acid.

In desert insects, the evaporation from respiratory surface is reduced to the minimum the internally invaginated spiracle system.

Where water is scarce, plants like cactus is a main source of water. These succulent plants have developed their own ways of storing water to help them tide through the dry days of the desert. Certain insects also depend on nectar from flowers and sap from stems to get water.

Kangaroo rats are known to produce water by digesting dry seeds.

Many rodents have extra tubules in their kidneys that help them extract most of the water from their urine and return it to the bloodstream. They also filter the moisture out of their exhaled breath through specialized organs in their nasal cavities.

A camel can tolerate a greater degree of water depletion of the body, and when water is available, it may drink more than one third of its body weight.

Hibernation is necessary for many ectodermic animals of the desert.

To Preserve Water

Reptiles, like the Gila monster, are known to store water in the fatty tissues in their tails and other parts of the body. Also, the hump of the camel has fatty tissue. When this fatty tissue is metabolized, it produces energy as well as water.

The reptiles have minimized the loss of water by excreting waste in the form of an insoluble white compound uric acid. This adaptation ensures very little wastage of water.

Most of the scavengers and the predators have evolved ways of extracting water from the food they eat.

Rodents of the desert stay in burrows during the day to avoid evaporation and water loss and conserve water by excreting highly concentrated urine and by not using water for temperature regulation.

Rodents of the desert can live on dry seeds, succulent cacti and other plants that store water and do not require drinking water.

Some special adaptive features

Poikilothermic animals, which match their internal temperature to the external, are adapted to live easily in the desert.

Protection of eye, ear and nostril against the sand is an important adaptation. In the burrowing snake, Typhlops, the eyes are covered by minute shields.

In camel, the eyes are well protected by long eye lashes and are kept high above die ground by long neck.

The ear opening of desert animals are also well protected by hair or scales.

The presence of poison glands is also an adaptive feature of desert animals.

Protection against natural enemies is achieved through protective colouration or spiny covering. Their colour generally matches with their surroundings.

The so-called homed lizard, Phrynosoma, of the western American deserts and the spiny devil, Moloch horridus, of Australia are classical examples of the desert animals having a spiny covering on their body.

Lizards use saliva regurgitated from the mouth over the throat region to achieve cooling.

A camel (Camelus dromedarius) in the desert uses several methods to reduce heat gain. Firstly, the heat is stored by an increase in body temperature. In camel deprived of water the body temperature in the morning may be about 34°C, which rises to 41”C in the late afternoon. This 7°C increase in body temperature corresponds to about 29000 kcal of heat, which equals a saving of 5 liters of water.

Further adaptations to desert life are splayed hooves, which are ideal for walking on sand and the hump which stores fat.

Thus, adaptations of desert animals are actually the adjustments to protect themselves against high temperatures, to live without water, and to conserve water as far as possible.

Sonoran Desert Tortoise

They store water in my bladder where it can be reabsorbed for use by their body during dry times.

Sonoran Desert Toad

They can survive in the desert because of their ability to excavate a burrow as much as three feet deep where they spend nine or ten months at a time. The spring rains "wake" them and they emerge from their burrow.

SPECIES AND SPECIAL ADAPTATION

American Kestrel

Scientists think that the dark colored patches under their eyes serve the same purpose as the black smudges athletes put on their face before playing outdoors. The black color absorbs bright sunlight so it does not reflect back up into the athlete's or the bird’s eyes. This allows me to be an active daytime hunter.

Kangaroo Rat

They do not ever need to drink water, even though their diet is almost entirely composed of dry seeds.

Jackrabbit

I have very large ears that are supplied with many blood vessels. This adaptation helps me to lose excess heat from my body.

Black Vulture

I will urinate (pee) on my legs if the daytime temperatures are over 70 degrees F. The urine will evaporate, cooling my legs and drawing more heat away from my body.

Bighorn Sheep

They have enlarged stomach compartments which can store enough water to last for several days, allowing them to go 2 or 3 days without a drink.

Gambel’s quail

Their “normal” body temperature is 107 degrees. This means that they can continue to be active during the heat of the day while losing body heat to the air until the outside temperature reaches 107 degrees.

Harris’ Antelope Ground Squirrel

They hold their tail arched over their back; this shades them, keeping them cooler. During hot weather they seek a cooler, shaded spot and will lie down, spreading their legs out to dump heat from their body.

Gila Monster

Their tail is a good indicator of their physical condition. A plump, well-rounded tail is the sign that they are a well-fed, healthy animal. A skinny, triangular-shaped tail indicates that they may be starving and dehydrated. Serving as a fat storage-locker, their tail is not detachable as is the tail of many other species of lizards. They can survive several years on the stored fat in their tails.

Costa’s Hummingbird

They begin breeding and nest building in late winter then migrate in late spring when temperatures become too hot.

Round-tailed Ground Squirrels

Because they are very dependent on succulent vegetation for moisture, they aestivate in their burrows for a few weeks during the summer drought, until the summer rainy season again brings new growth.

SUMMARY

The Xerophytes are subjected to extreme heat and dryness, and the desert’s harsh environment. The deserts are very hot during the day but will cool during the evening. There is constant sunlight almost daily. Xerophytes exhibit a range of adaptations that enable them to survive in this arid environment.The plant adaptation includes modification of stem andleaf to avoid evapouration and unwanted water lose. Succulents ,like the cactus, store water in their leaves or stem. In many plants the leaves are modified to form spines. This helps them to deter browsing animals and avoids excess transpiration during day time. The anatomical features of these plants include the presence of cuticle,heavily thickened cell walls, fleshy roots to store water etc.The adaptations of xerophytic animals include Hygroscopic skin ,presence of cuticle,spines and poison glands. Many animals are nocturnal ,i,e.they are active during night.They dig holes and burrows in the sand and live within. They also have good water storage system. The xerophytic animals includes camel, kangaroo rat ,black vulture etc.