Unit - 3, Organisms and their Structure

 Unit - 3, Organisms and their Structure

  1. Tick (V) the correct alternative given below. a. In which phylum a snail lies?
  • iv. Mollusca (√) b. Animals of which phylum of the following are found only in ocean?
  • iii. Echinodermata (√) c. Which one is a unicellular animal?
  • iii. Paramecium (√) d. Which of the following is a character of a cylindrical and unsegmented body?
  • ii. Body is covered with cuticle (√) e. Which of the following is a unisexual parasite having a cylindrical and unsegmented body?
  • ii. Ascaris (√) f. Which of the following is the main characteristic of the phylum of prawn?
  • iii. Segmented body (√)
2. Fill in the blanks using the suitable words given below: Tentacles bisexual Annelida Porifera Protozoa |
a. The animals having cylindrical and segmented body are kept in the Phylum Annelida.
b. Flat animals are Platyhelminthes.
c. Sponges are kept in phylum Porifera.
d. All the single-celled animals are grouped in Protozoa.


3. Answer the following questions:
a. Write the name of the phylum of following animals.
* Leech: Annelida
* Prawn: Arthropoda
* Starfish: Echinodermata
* Earthworm: Annelida
* Euglena: Protozoa

b. A butterfly is grouped in phylum Arthropoda because it has jointed legs and a segmented body, which are characteristic features of this phylum.

c. Three characteristics of phylum Protozoa:
* Unicellular organisms
* Lack of tissues and organs
* Reproduce asexually (mostly)

d. Sponges are grouped in phylum Porifera. They are simple, aquatic animals that have pores all over their bodies.

e. Two phyla with bisexual animals:
* Platyhelminthes (flatworms)
* Annelida (segmented worms)

f. Similarity between flatworms and cylindrical worms:
* Both are invertebrates.

Difference between flatworms and cylindrical worms:
* Flatworms have a flat, bilaterally symmetrical body.
* Cylindrical worms have a cylindrical, bilaterally symmetrical body.

g. Three characteristics of animals in phylum Mollusca:
* Soft, unsegmented body
* Muscular foot
* Most have a hard shell

(h) Differentiate between

i. Protozoa and Porifera

ProtozoaPorifera
Unicellular organismsMulticellular organisms
Lack a body organizationHave a simple body organization
Found in aquatic or moist environmentsMostly marine, some freshwater species
Have locomotory structures like cilia, flagella, or pseudopodiaSessile; do not move from place to place
Examples: Amoeba, ParameciumExamples: Sponges

ii. Arthropoda and Mollusca

ArthropodaMollusca
Exoskeleton made of chitinBody covered by a calcareous shell
Segmented body with jointed appendagesUnsegmented body, soft and muscular
Open circulatory systemOpen or closed circulatory system
Examples: Insects, spiders, crabsExamples: Snails, clams, octopus

iii. Earthworm and Pinworm

EarthwormPinworm
Belongs to the phylum AnnelidaBelongs to the phylum Nematoda
Body is segmentedBody is cylindrical and unsegmented
Free-living in soilParasitic, living in the intestine of host
HermaphroditeSeparate sexes

iv. Ascaris and Leech

AscarisLeech
Phylum: NematodaPhylum: Annelida
Cylindrical, unsegmented bodySegmented body with clitellum
ParasiticMostly ectoparasitic, some are free-living
Separate sexesHermaphrodite

(i) Sketch Neat Diagrams of the Following

Here are basic descriptions for drawing:

  1. Amoeba: Irregular shape with pseudopodia, nucleus, food vacuoles.
  2. Earthworm: Cylindrical, segmented body, clitellum visible.
  3. Snail: Spiral shell, head with tentacles and eyes, muscular foot.
  4. Hydra: Tube-like body with tentacles radiating from the top.

(j) Why are Ascaris and Earthworm Classified into Different Phyla?

Ascaris (phylum Nematoda) and earthworm (phylum Annelida) look similar superficially but differ significantly in their anatomy and physiology:

  1. Body Segmentation:
    • Earthworm has a segmented body, whereas Ascaris has a cylindrical, unsegmented body.
  2. Body Cavity:
    • Earthworm has a true coelom (body cavity), while Ascaris has a pseudocoelom.
  3. Mode of Life:
    • Earthworms are free-living organisms, while Ascaris is parasitic.
  4. Reproductive System:
    • Earthworms are hermaphroditic, whereas Ascaris has separate sexes.
  5. Nervous System:
    • Earthworms have a well-developed nervous system; Ascaris has a simpler one.

These differences justify their placement in separate phyla.


(4) Answer the Following Questions

a. Define cell:
The cell is the basic structural and functional unit of life. It is the smallest unit capable of performing all life processes.

b. Why are cells considered the basic unit of life?
Cells are considered the basic unit of life because:

  1. All living organisms are made up of cells.
  2. Cells perform essential life processes such as growth, metabolism, and reproduction.
  3. The activities of an organism are the sum of the activities of its individual cells.

c. Which component of a cell is called the powerhouse of a cell?
The mitochondria are called the powerhouse of the cell because they generate energy in the form of ATP (adenosine triphosphate) through cellular respiration.

d. Sketch neat diagrams of animal and plant cells and label their parts:

  • Plant cell: Draw a rectangular shape with structures like a cell wall, cell membrane, nucleus, chloroplasts, vacuole, cytoplasm, and mitochondria.
  • Animal cell: Draw an oval shape with structures like a cell membrane, nucleus, cytoplasm, mitochondria, and small vacuoles.

(6) Mention the components found in an animal cell:

The components of an animal cell include:

  1. Cell membrane
  2. Cytoplasm
  3. Nucleus
  4. Mitochondria
  5. Ribosomes
  6. Endoplasmic reticulum (smooth and rough)
  7. Golgi apparatus
  8. Lysosomes

f. Write any four components found in cytoplasm:

  1. Ribosomes
  2. Endoplasmic reticulum
  3. Mitochondria
  4. Golgi apparatus

g. Why is the plant cell selected for studying cell structure?

Plant cells are often selected for studying cell structure because:

  1. They have distinct and visible structures like the cell wall, chloroplasts, and a large central vacuole, which are not present in animal cells.
  2. The rigid cell wall makes the shape of the cell easier to observe under a microscope.
  3. Plant cells are generally larger and more uniform in shape compared to animal cells, making them suitable for educational study.
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