30 Transport Systems in Plants-Mid

Transport Systems in Plants FOCUS Question How do plant cells work together to move nutrients?

植物中的运输系统聚焦问题植物细胞如何协同工作来运输营养物质?

From Tiny to Tall Imagine Earth without bushes or trees. Millions of years ago, the only plants were tiny and low to the ground, like the mosses of today. These were nonvascular plants plants— with no special system of tubes and tissues to move water and nutrients. A plant won't grow taller if the upper part of the plant can't get what it needs to survive. Today, a vast variety of plants cover Earth! Vascular plants have tubes in their roots, stems, and leaves to move nutrients, food, and water. With this transport system, vascular plants, like giant redwood trees, can grow taller than 90 meters (300 ft.) That's a long way to move water, food, and nutrients. Wowser! The world's tallest tree is Hyperion, a tree in Redwood National Park in California. It's approximately 116 meters (381 ft.) tall.

想象一下没有灌木丛或树木的地球。 数百万年前，唯一的植物都很小，而且低矮，就像今天的苔藓一样。 这些是无维管植物——没有特殊的管道和组织系统来输送水分和营养物质。 如果植物的上部得不到生存所需的养分，它就不会长高。 今天，地球上覆盖着种类繁多的植物!维管植物的根、茎和叶都有管子，用来输送营养物质、食物和水。 有了这个运输系统，维管植物，比如巨大的红木，可以长到90米(300英尺)以上。这是一段很长的路来运输水、食物和营养物质。 老古板!世界上最高的树是加州红木国家公园里的亥伯龙。 它大约116米(381英尺)高。

Flow Through Plant Parts You probably know the main parts. of a plant But do you know how they each move water, food, and nutrients throughout the plant? Roots Roots not only anchor a plant in the ground; they pull water and nutrients from the soil. There are many tiny hairs on the roots, called root hairs, which help absorb water. One hair can't absorb a lot, but think how much water thousands of hairs can absorb. Roots also provide storage for the plant. Food is made in the leaves and flows down toward the roots. Plants use food to grow and maintain their tissues. They store extra food in their roots in the form of starch for times when they aren't able to make new food.

你可能知道植物的主要部分。 但是你知道它们是如何在植物中传递水、食物和营养物质的吗? 根不仅把植物固定在地上;它们从土壤中吸收水分和养分。 根上有许多细小的毛发，称为根毛，有助于吸收水分。 一根头发不能吸收很多，但想想成千上万根头发可以吸收多少水。 根也为植物提供储存空间。 食物在叶子中产生并流向根部。 植物需要食物来生长和维持它们的组织。 当它们不能制造新的食物时，它们会以淀粉的形式将额外的食物储存在根部。

Leaves Leaves differ greatly in size and shape They can be single, simple leaves or clusters of small leaflets called compound leaves. Even the needles on a pine tree and the spines on a cactus are leaves. Leaves gather sunlight and carbon dioxide from the air. They combine it with water to make sugars, the food for the plant. This process is called photosynthesis. Veins in a leaf bring in water and minerals. The veins also send food from the leaf to other parts of the plant. Tiny holes in the leaf let gases flow, letting carbon dioxide in and oxygen out. These holes are called stomata. Water exits stomata through the process of evaporation. This special kind of evaporation used by plants is called transpiration.

叶子在大小和形状上有很大的不同。它们可以是单叶，也可以是称为复叶的小小叶簇。 甚至松树上的针和仙人掌上的刺都是叶子。 树叶从空气中收集阳光和二氧化碳。 它们将其与水结合生成糖，这是植物的食物。 这个过程叫做光合作用。 叶脉带来水分和矿物质。 叶脉也把食物从叶子输送到植物的其他部位。 树叶上的小孔让气体流动，让二氧化碳进入，氧气排出。 这些孔叫做气孔。 水通过蒸发过程排出气孔。 植物利用的这种特殊的蒸发作用叫做蒸腾作用。

Stems The stem holds the plant upright and connects the roots to branches and leaves. Within the stem of vascular plants are special tissues that transport substances throughout the plant. The xylem (ZY-lum) moves water and minerals from the roots to the leaves. Xylem cells are long and thin. They die soon after they form, but their hard structure remains. Xylem cells form a pipeline from the roots to the stem or trunk. The pipeline splits off into branches and moves into every leaf. Do You Know? When you observe tree rings, you are looking at the remains of old xylem tissue.

茎使植物直立，并将根与树枝和叶子连接起来。 在维管植物的茎内有特殊的组织，在整个植物中运输物质。 木质部(ZY-lum)将水和矿物质从根转移到叶子。 木质部细胞又长又薄。 它们在形成后不久就会死亡，但它们坚硬的结构保留了下来。 木质部细胞形成一条从根到茎或干的管道。 管道分裂成分支，进入每一片叶子。 你知道吗?当你观察树木年轮时，你看到的是古老木质部组织的残余。

The phloem (FLOW-um) carries food from the leaves to other parts of the plant. Phloem cells are long and connected to one another throughout the entire plant. Unlike xylem cells, phloem cells remain alive for the life of the plant. In trees, the phloem is the innermost part of the bark. It must not be damaged or the tree might die. In some plants, the xylem and phloem are scattered throughout the plant in no particular order. In others, xylem and phloem are arranged in a ring around the edge.

韧皮部(FLOW-um)将食物从叶子运送到植物的其他部位。 韧皮部细胞长且在整个植物中相互连接。 韧皮部细胞与木质部细胞不同，韧皮部细胞在植物的一生中都是存活的。 在树木中，韧皮部是树皮最里面的部分。 它不能被损坏，否则树可能会死。 在一些植物中，木质部和韧皮部分布在整个植物中，没有特别的顺序。 在其他植物中，木质部和韧皮部沿边缘呈环状排列。