Transcript Document
20.1 Origins of Plant Life KEY CONCEPT Plant life began in the water and became adapted to land. 20.1 Origins of Plant Life Land plants evolved from green algae. • Plants and green algae have many common traits. – both are photosynthetic eukaryotes – both have the same types of chlorophyll – both use starch as a storage product – both have cell walls with cellulose 20.1 Origins of Plant Life • Genetic analysis points to the common ancestor of all plants. – extinct green algae species in class Charophyceae – modern charophyceans common in lakes and ponds 20.1 Origins of Plant Life • Important plant characteristics likely originated in charophyceans. – multicellular body allowing for specialization of cells and tissues – cell division that allows for chemical communication between cells – reproduction involving sperm swimming to egg 20.1 Origins of Plant Life • True plants evolved through natural selection. – Ancestral charophyceans lived in areas of shallow water. – Those that could survive longer dry periods were favored. – First true plants probably grew at edges of water. – True plants have embryos that develop while attached to female parent. 20.1 Origins of Plant Life • True plants evolved through natural selection. 20.1 Origins of Plant Life Plants have adaptations that allow them to live on land. • Challenges of living on land have selected for certain plant adaptations. • A cuticle allows plants to retain moisture. – waxy, waterproof layer – holds moisture in 20.1 Origins of Plant Life • Stomata are tiny holes in the cuticle. stoma – can open and close – allow air to move in and out 20.1 Origins of Plant Life • A vascular system allows resources to move to different parts of the plant. – collection of specialized tissues – brings water and mineral nutrients up from roots – disperses sugars from the leaves – allows plants to grow higher off the ground water and mineral nutrients sugars 20.1 Origins of Plant Life • Lignin allows plants to grow upright. lignin plant cells – hardens cell walls of some vascular tissues – provides stiffness to stems 20.1 Origins of Plant Life • Pollen grains allow for reproduction without free-standing water. – pollen grains contain a cell that divides to form sperm – pollen can be carried by wind or animals to female structures 20.1 Origins of Plant Life • A seed is a storage device for a plant embryo. – seed coats protect embryos from drying wind and sunlight – embryo develops when environment is favorable 20.1 Origins of Plant Life Plants evolve with other organisms in their environment. • Plants and other organisms can share a mutualistic relationship. – a mutualism is an interaction in which two species benefit – plant roots and certain fungi and bacteria – flowering plants and their animal pollinators 20.1 Origins of Plant Life • Plants have adaptations that prevent animals from eating them. – spines and thorns – defensive chemicals