In amoeba, all functions are carried out by the single cell. Especially when amoeba ingests food through phagocytosis or pinocytosis then it makes a vacuole around the food particle. The vacuole in amoeba is contractile in nature. This contractility is important to accommodate food of various sizes and to have enough digestive enzymes. Moreover, amoeba being an aquatic animal the contractile vacuole helps in maintaining the tonocity of the cell as well.

Interaction of molecules within the membrane, intercellular functions, secretion, endocytosis are the advantages of lipid bilayer fluidity.

Endoplasmic reticulum, Golgi apparatus are the organelles with permeable biomembrane.

The different types of plastids leucoplasts chromoplasts chloroplasts such as are interchangeable. The transformation from chloroplasts is observed during ripening of fruits (e.g Tomato, Chilli) when they change their color from green to reddish orange. It takes place through loss of chlorophylls and degeneration of lamellae. The most common carotenoid of the fruit is lycopene. Petals of Calendula develop orange yellow color due to the formation of chromoplasts from proplastids.
Carrot root develops it characteristic color because of the conversion of leucoplasts into chromoplasts.It is rich in carotene.

All organisms begin their life as a single cell. Certain organisms are made up of single cell only. They are called unicellular or acellular organisms, e.g., Amoebe Chlamydomonas, bacteria and yeast.
In other organisms, single cell undergoes divisions to from multicellular body. Body of human being is made up of trillion of cells. All the cells of an organism carry the same genetic material, developed from same pre-existing cells and possess several organelles to perform various life activities. The cells are therefore, basic unit of life and structural unit of an organism.

It means that 9 microtubule doublets surround two single microtubules.

The sticky layer of cell envelope is called glycocalyx. It is also known as mucilage sheath.

Gas vacuoles are name so, because these are permeable to atmospheric gases and not to water

On the outer and inner surface of phospholipid matrix.

Following are the labelled sections of cell membrane 
A - Cholesterol
B - Glycolipid
C - Hydrophilic head of phospholipid
D - Hydrophobic tail of phospholipid
E - Transmembrane protein
F - Intrinsic protein

Characteristics of prokaryotic cells are as follows
(i) A prokaryotic cell, i.e., of bacteria is surrounded by a cell membrane. The cell wall in turn is surrounded by a slimy layer.
(ii) Absence of well-organised chloroplast, mitochondria and nucleus.
(iii) Nucleolus is absent. It is known as nucleoid. The DNA of a prokaryotic cell is circular and not associated with basic proteins.
(iv) The cytoplasm is filled with dense granules. Most of these granules are ribosomes.
(v) A prokaryotic cell possesses single chromosome (not paired) that exists as circular loops of DNA without histone proteins.

An animal cell has following cell structures:
i) Plasma membrane
ii) Endoplasmic reticulum
iii) Mitochondria
iv)Golgibody
v) Lysosomes
vi) Ribosomes
vii) Vacuoles
viii) Nucleus
ix) Centriole
           
Plasma Membrane.
This is also known as cell membrane. Plasma membrane is made up of lipid and protein. It is semi-permeable in nature. Certain substances are transported through plasma membrane by passive transport. Some substances get transported by osmosis and some by active transport. Active transport involves use of some carrier to facilitate transport. Apart from transport of materials, plasma membrane gives a shape and size to the animal cell.
Endoplasmic Reticulum.
These are networks of fine tubules extending from plasma membrane to nucleus. They work like pipelines and facilitate transport of substances from outside the cell to nucleus and cytoplasm. Depending on presence or absence of ribosomes ER can be either rough or smooth.
Golgi Body.
This is composed of many sack like structures stacked one over another. The function of golgi body is to package different materials, like carbohydrate, protein and lipid.
Lysosome.
Lysosome is small spherical structure filled with digestive enzymes. The digestive enzyme helps in digesting foreign materials and waste products. Sometimes the lysosome digests the contents of cytoplasm which in turn kills the cell itself. That is why lysosome is also known as 'suicide bag of the cell'.
Ribosome.
Ribosomes are small dot like structures. They are made of two subunits. The function of ribosome is to synthesize protein.
Vacuoles.
These are small fluid filled structures. Vacuoles help in maintaining osmotic pressure inside the cell.
Mitochondria.
Mitochondria is double membrane structure. The inner membrane is projected in finger-like structures, called cristae. The presence of cristae helps in increasing the inner surface are of mitochondria. Aerobic respiration takes place in the mitochondria and energy released is stored in the form of ATP (Adenosine triphosphate).
Nucleus.
Nucleus is covered by nuclear membrane. Nucleus contains chromosomes which are genetic materials. Nucleus also controls various functions of the cell.
Centriole.
These are spindle like structures. During cell division they form spindle fibres.

Every chromosome essentially has a primary constriction or the centromere on the sides of which disc-shaped structures called kinetochores are present. Based on the position of the centromere, the chromosomes can be classified into four types.
Metacentric Chromosome : The metacentric chromosome has middle centromere forming two equal arms of the chromosome. Sub-metacentric Chromosome. The sub-metacentric chromosome has centromere nearer to one end of the chromosome resulting into one shorter arm and one longer arm.
             
Acrocentric Chromosome : In case of acrocentric chromosome, the centromere is situated close to its end forming one extremely short and one very long arm, Telocentric Chromosome. The telocentric chromosome has a terminal centromere.