Pollen vs Spore
Diploid spore mother cells give rise to spores. Spores are haploid structures. They are important for reproduction as well as for survival in the unfavorable conditions. Spores are seen as a part of the life cycle of many organisms including plants, fungi, bacteria, algae etc. In plants, depending on the different types of spores, a plant can be homosporous or heterosporous. If the plant has only one type of spores, it is known as homospory. If the plant has two types of spores that are male and female spores, it is known as heterospory.
Almost all seed bearing plants are heterosporous. They possess large spores, which are called megaspores in the megasporangium, and small spores, which are called microspores in the microsporangium. As the spores grow they become gametophytes. The megaspores become female gametophytes and the microspores become the male gametophytes. Unlike in primitive plants, in seed bearing plants, the gametophytes are never released from the spore. This can be considered as an evolutionary advance. Due to this nature the gametophytes are well protected from desiccation. But the male sperms produced from the male gametophyte needs to reach the female egg. This is done through the dispersal of spores. Spores can be dispersed by wind, water, or insects.
Male spores are called microspores. Microspores are also called pollen grains. In flowering plants, microspores are found inside the pollen sac or the microsporangium. Microspores are very small, minute structures. They are almost like dust particles. Each microspore has one cell and two coats. Outermost coat is the extine, and the inner one is the intine. Extine is a tough, cutinized layer. Often it contains spinous outgrowths. Sometimes it can be smooth, as well. The intine is smooth, and it is very thin. It is mainly made up of cellulose. The extine contains one or more thin places known as the germ pores through which the intine grows out to form the pollen tube. The pollen tube elongates trough the gynoecium tissues carrying two male gametes in it. Pollen tube grows down and enters the ovule through the micropyle. Then the apex of the pollen tube degrades and the two male nuclei are released in to the ovule. Double fertilization takes place by the fusion of the one male nucleus with the egg cell nucleus, giving rise to the diploid zygote, and fusion of the other male nucleus with the diploid secondary nucleus giving rise to the triploid primary endosperm nucleus.
What is the difference between Spores and Pollens?
• Spores are reproductive haploid structures and which can be large female spores, which are called megaspores, or small male spores, which are called microspores (pollens). In other words, all pollens are spores, but not all spores are pollens.
• Pollens are produced from the microspore mother cells, but female spores are produced by the megaspore mother cells.
• Pollen grains have two outer coats extine and intine and female spores do not have the extine or intine.
• Pollens are dispersed by various mechanisms, but female spores are retained within the ovary.
• Pollens are found inside the pollen sac, and female spores are found inside the ovule.