Vacuoles and lysosomes are membrane bound organelles of a cell that possess varieties of enzymes with the help of which they degrade different biomolecules.
Usually, vacuoles are exclusively found in plant and fungi cells. Some protist, animal and bacterial cells possess vacuoles as well. Lysosomes, on the other hand, are generally found in animal cells but can be found in some plants cells as well.
As, both these organelles perform similar functions, they are not usually present in a cell at the same time. Let us discuss how and why they are similar and different from each other along with some of its functions.
Functions of vacuoles and lysosomes
Both vacuoles and lysosomes perform diverse functions in a cell and have a lot in common. Let us discuss it in detail.
Vacuoles and lysosomes, both possess a variety of hydrolases. So, their basic function is to digest and breakdown different biomolecules to their basic structures. Apart from that these organelles also perform various different functions.
Major functions of vacuoles
Vacuoles are organelles enclosed within a tonoplast that occupy nearly 90% of the plant cells by volume. Let us discuss the functions of vacuoles in details.
- Turgor Pressure: Vacuoles accumulate a lot of organic and inorganic salts in order to maintain the cell turgidity. High salt concentration inside the vacuoles causes endosmosis of water molecules inside the vacuoles. This causes the tonoplast to stretch and press the cell contents against the call wall. Turgor pressure is needed by the non woody plants or parts of the plants for rigidity.
- Storage: Vacuoles act as the depositories for several biomolecules such as proteins, secondary metabolites and the metabolic waste products released by the cells. Several water-soluble pigments such as anthocyanins and betanin along with several secondary products are sequestered in the vacuoles.
- Recycling during senescence: Vacuole possess several hydrolytic enzymes which can degrade different biomolecules present in the cells and also cellular components such as cell organelles. Degradation of these materials release simple and precursor biomolecules that can be reused by the plant after a cell’s death.
- Waste disposal: Vacuoles also act as the store house for waste products or xenobiotic compounds which do not get metabolized by the cells such as heavy metals, fertilizers, pesticides, herbicides and insecticides.
- Defense: Vacuoles store several secondary metabolites that can prove to be toxic to herbivores, pathogens, parasites and the plant itself. An example is storage of calcium oxalate crystals in the vacuoles of the plant Dieffenbachia. Contact with the cell sap of this plant can lead to undesired effects.
- Contractile Vacuole: These are specialized vacuoles responsible for osmoregulation in the cells. They pump out water or fluids containing high concentration of potassium and sodium ions, from the cells of fresh water protists that do not possess a cell wall. An example is the contractile vacuoles present in the fresh water Chlamydomonas species.
Major functions of lysosomes
Similar to vacuoles, lysosomes are membrane bound organelles possessing an array of enzymes. Let us discuss their functions in details.
- Food Digestion: Lysosomes contain a of different enzymes that can help a cell digest proteins, nucleic acids, polysaccharides and lipids taken up by endocytic, secretory autophagic and phagocytic processes.
- Recycling: After the degradation of phagolysosomes, autophagosomes and endocytosed macromolecules, the resultant products are transported to the cytoplasm. These products then are converted to basic constituents of biomolecules for reuse by the cell.
- Phagocytosis: Specialized cell such as macrophages engulf cell debris, microbes and other antigenic materials that need to be eliminated from the body. These form a phagosome which then fuses with the lysosomes to form phagolysosomes. The lysosomal enzymes then degrade these particles.
- Secretory Lysosomes: Found in specific cell types such as hemopoietic cells, macrophages, microglia and melanocytes, secretory lysosomes are involved in pigmentation, coagulation, wound repair, and immunologic functions.
- Autophagy: It is a regulated cell death process where cytoplasmic components are degraded by the lysosomes. It occurs in response to stress or signals. The first step involves formation of autophagosome by engulfment of cellular organelles. This then fuses with the lysosome for degradation of the cellular components.
- Repair and wound healing: Cell membrane allows influx of calcium ions from outside the cell membrane, upon being wounded. High concentration of calcium ions triggers cell death response. To prevent the cell from death, lysosomes fuse with the plasma membrane and release their components in the extra cellular matrix.
Similarities between vacuoles and lysosomes
Vacuoles and lysosomes are very similar to each other in terms of their functions. Let us discuss more about this.
|Membrane||Membrane bound organelle.||Membrane bound organelle.|
|Contents||They possess multiple hydrolytic enzymes that can degrade all sorts of biomolecules, cellular and non-cellular materials.||They also possess multiple hydrolytic enzymes that can degrade all sorts of biomolecules, cellular and non-cellular materials.|
|Functions||Degradation of biomolecules.|
Storage of biomolecules.
Recycling of biomolecules.
|Degradation of biomolecules.|
Storage of biomolecules.
Recycling of biomolecules.
|Autophagy||They can cause cell death by releasing hydrolytic enzymes into the cytoplasm.||They can also degrade cellular components and cause cell death by releasing the stored enzymes.|
Differences between vacuoles and lysosomes
Although vacuoles and lysosomes are very similar to each other, they have a fair share of differences. Let us discuss those differences.
|Location||Plants and fungi cells.||Animal cells.|
|Exceptions of location||Present in some bacterial, protist and animal cells.||Absent in red blood cells.|
|Size||Comparatively bigger in size. Occupies 90% of the plant cell.||Small in size.|
|Number||Usually, plants have one large and main vacuole and may possess some small ones.||Lysosomes are multiple in number in a single cell.|
|Autophagic vesicles||Engulfs autophagosomes.||Fuses with autophagosomes.|
|Membrane dynamics||Tonoplast does not undergo fusion and fission with other organelles or plasma membrane.||Membrane undergoes fusion and fission with other organelles and plasma membrane.|
|Internal pH||5.5 – 6.2||4.5 – 5.5|
|Formation||Formed by the biosynthetic pathways of endoplasmic reticulum and Golgi compartments, endocytosis of substances from plasma membrane and autophagy.||Formed from fusion of endosomes with transport vesicles that bud out from trans Golgi network.|
|Functions||Turgor pressure maintenance,||Cell signaling and transportation, secretory functions, membrane repair,|
Are vacuoles and lysosomes same
Although vacuoles and lysosomes share some properties and have similar functions, they are different organelles.
Vacuoles and lysosomes are one and the same based on their very similar functions. Also, both these organelles are usually not present in a cell at the same time. Hence, it can be said that they take over each other’s functions.
Although lysosomes and vacuoles have some structural differences, they basically perform a similar set of functions in a cell.