Unit 2.4 - Nutrition in unicellular organisms

What type of nutrition do protoctista such as amoeba use?

Holozoic nutrition

What type of organism are amoeba having what type of surface area to volume ratio?

They are unicellular organisms that have a large surface area to volume ratio

In amoeba, how are nutrients absorbed?

Across the cell membrane by diffusion, facilitated diffusion or active transport

In amoeba, how are large molecules and microbes ingested?

By endocytosis into food vacuoles

In amoeba, what do the food vacuoles fuse with?

Lysosomes - contents digested by lysosomal enzymes, indigestible remains get tested by exocytosis

How do amoeba engulf food?

By phagocytosis - the cell invaginated food via the pseudopodia in the cell membrane

• The amoeba then stores food in a vacuole, at this point the food is not considered inside the cell, it is stored in a vacuole but because it hasn't been absorbed into the cytoplasm, it is not inside the cell

• The amoeba digests the food with digestive enzymes and then absorbs the nutrients

What happens in the first stage of holozoic nutrition in amoeba?

In ingestion, finger like projections called pseudopodia surround the food

• The pseudopodia attach to each other forming a food vacuole (endocytosis)

• The food vacuole now contains the food and some of the water medium

What happens in the second stage of holozioc nutrition in amoeba?

In digestion, the food vacuole fuse with lysosomes

• The lysosomal enzymes digest the contents of the food vacuole

• Digestion is carried out intracellularly

What happens in the third stage of holozoic nutrition in amoeba?

In absorption, the products of digestion are absorbed into the cytoplasm by diffusion

What happens in the fourth stage of holozoic nutrition in amoeba?

In assimilation, the absorbed food particles may be stored as glycogen and lipids

• They may be used as an energy source to hold and maintain life processes or they may be converted into other chemicals such as those required as part of the structure

What happens in the fifth stage of holozoic nutrition in amoeba?

In egestion, indigestible materials are egested by exocytosis