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Plant Biology - Bryophytes—The Non‐Vascular Plants

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    Study Guide Plant Biology – Bryophytes — The Non ‐ Vascular Plants 1. A Typical Bryophyte Life Cycle Even though mosses, liverworts, and hornworts look different, their life cycles follow the same basic pattern . The diagram above shows a moss life cycle, which represents bryophytes in general. 1. 1 Alternation of Generations: The Big Idea Bryophytes show alternation of generations . This means they have two main stages in their life cycle: • Gametophyte (haploid, 1n) → produces gametes (sperm and egg) • Sporophyte (diploid, 2n) → produces spores In bryophytes, the gametophyte is the dominant, green, and independent plant you usually see.

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    Study Guide 1. 2 From Spores to Protonema (Refer to the upper - left part of the image) • The life cycle begins with haploid spores (1n) . • Each spore can grow into a thin, green, thread - like structure called a protonema . • The protonema looks like algae and spreads over the surface. • In many mosses, protonemata form dense green mats with rhizoids and upright filaments. • Under suitable conditions (like red light and kinetin ), cells of the protonema develop buds . These buds grow into leafy shoots , which become mature gametophytes . 1. 3 Gametophyte: The Main Plant (Refer to the central upper part of the image) • The mature gametophyte is photosynthetic and independent . • It produces special reproductive structures called gametangia . There are two types: • Antheridia (male) → produce sperm • Archegonia (female) → produce eggs These structures may be found: • On the same plant , or • On different plants Both antheridia and archegonia have a protective sterile outer layer , which helps protect the gametes. This feature is an important evolutionary step compared to algae.

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    Study Guide 1. 4. Fertilization Needs Water (Refer to the right side of the image) • When rain or dew is present, mature sperm are released from antheridia. • The sperm are biflagellate and motile , meaning they can swim. • They swim through the thin film of water to reach the archegonium. • One sperm fuses with the egg → this process is called fertilization . This type of reproduction is called oogamy , where: • The egg is large and non - motile • The sperm is small and motile Important point: Bryophytes require external water for fertilization , unlike higher plants where sperm travel through pollen tubes. 1.5 Zygote and Embryo Formation (Refer to the lower - right part of the image) • Fertilization forms a diploid zygote (2n) . • The zygote stays inside the archegonium. • It divides by mitosis to form a multicellular embryo . • This embryo develops into the sporophyte . The gametophyte supplies food to the developing sporophyte. This nourishment is called matrotrophy . • No plasmodesmata connect the two generations. • Nutrients move along the cell walls (apoplastic movement) .

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    Study Guide 1 . 6 Structure of the Sporophyte (Refer to the lower - left and central parts of the image) In mosses and liverworts, the mature sporophyte has three parts: • Foot → anchors the sporophyte to the gametophyte • Seta → stalk that lifts the capsule • Capsule (sporangium) → produces spores In mosses: • A protective cap called the calyptra covers the developing capsule. • The capsule has: o Operculum (lid) o Peristome teeth that help in controlled spore release • Inside the capsule, sterile cells called elaters respond to moisture. o They twist and untwist as they absorb and lose water. o This movement helps push spores out into the air. 1 . 7 Spore Formation and Release (Refer to the capsule region in the image) • Inside the capsule, spore mother cells undergo meiosis . • This produces haploid spores (1n) . • Spores are released and dispersed by wind. • When they land in a suitable place, the cycle begins again. 1 . 8 Special Case: Hornwort Sporophyte • In hornworts, the sporophyte is: o Long, green, and cylindrical o Photosynthetic o Provided with stomata

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